Pedro Martinez at his peak was arguably the most unhittable starting pitcher in Major League Baseball history, but where does Martinez rank on Bleacher Report's list of the 10 greatest ever?

More than 75 pitchers have been inducted into the MLB Hall of Fame, so how does one pick the best of the best? And are there any current hurlers who stack up well against the retired greats?

To answer those questions, we ranked dozens of starting pitchers in five categories:

• Career ERA
• Career K/BB*
• Career WAR**
• Postseason Success
• Dominance During Five-Year Peak

*Strikeout rate per inning has changed drastically throughout the history of the game, but strikeout-to-walk (K/BB) ratio is a rather consistent measure of a pitcher's effectiveness. Whether you're talking 1889, 1936 or 2014, a 2.5 K/BB ratio is strong, anything better than a 3.0 is great and pitchers above 4.0 are just plain lethal.

**WAR gives a great snapshot of how great a pitcher was compared to the rest of the league during his era. WAR is calculated differently on various sites. We used FanGraphs' version.

Scores in those five categories were summed to create one cumulative ranking.

Not surprisingly, most of the top candidates also rank in the top 20 in career WAR. However, two pitchers from outside the top 50 in career WAR made it into our top 10, so there's much more than just one metric at play.

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Honorable Mentions

Nolan Ryan (1966-93, 324 wins, 3.19 ERA, 2.05 K/BB)

It's shocking that the all-time strikeout leader and the man with seven no-hitters couldn't statistically sneak into the top 10, but Ryan's legacy was more about longevity than any particular stint of dominance. A career walk rate of 4.67 per nine innings doesn't help Ryan's case, but even if we had emphasized K/9—Ryan's mark was 9.55—instead of K/BB, he still would have fallen a bit shy of 10th place.

Bert Blyleven (1970-92, 287 wins, 3.31 ERA, 2.80 K/BB)

Similar to Ryan, Blyleven was a workhorse who became revered for sticking around for as long as he did. He logged nearly 5,000 innings in a career that spanned more than two decades, but his ERA and strikeout rate weren't anything special compared to those who made the cut. It took 14 years of eligibility before he got inducted into the Hall of Fame, which should serve as proof that he's not one of the 10 greatest starting pitchers in the sport's history. He's not far from that list, though.

Tom Seaver (1967-86, 311 wins, 2.86 ERA, 2.61 K/BB)

Seaver wasn't much better than league average for his final eight seasons, which ended up negatively impacting his career ERA and K/BB numbers. But his first 12 years (2.51 ERA, 3.10 K/BB) were nothing short of remarkable. Much (if not all) of that time overlapped with the careers of Steve Carlton, Gaylord Perry, Fergie Jenkins, Phil Niekro and a few other Hall of Famers, yet Seaver was the best of the bunch.

Lefty Grove (1925-41, 300 wins, 3.06 ERA, 1.91 K/BB)

Grove had the misfortune of pitching during the hitter-friendly 1930s, making his ERA and K/BB pale in comparison to most of the other candidates for this list. It should be noted, however, that he's the only guy anywhere close to our top 10 who appeared in a single game between 1931 and 1942. Save for an injury-caused blip in 1934, he was almost unhittable compared to other pitchers of that era. Grove led the American League in ERA nine times from 1926 to 1939.

Grover "Pete" Alexander (1911-30, 373 wins, 2.56 ERA, 2.31 K/BB)

Tied for third on MLB's all-time wins list with 373, Alexander was dominant for a decade. Were it not for World War I limiting him to three appearances in 1918, he likely would have eclipsed 400 victories. However, his career K/BB ratio leaves something to be desired, and he never got much of a chance to pitch in the postseason.

10. Bob Gibson (1959-1975)

Career Stats: 251-174, 3884.1 IP, 2.91 ERA, 7.22 K/9, 3.10 K/BB, 82.3 WAR

Five-Year Peak: 1968-72

Bob Gibson was great for his first nine seasons, but he was so dominant in 1968 that Major League Baseball was forced to change pitching rules to improve scoring. In winning the NL MVP and the first of his two Cy Young Awards, Gibson had a mind-boggling 1.12 ERA with 13 complete-game shutouts in 34 starts. He also had a league-best 268 strikeouts.

That offseason, the pitcher's mound was lowered by five inches and the size of the strike zone was reduced, but Gibson continued to dominate. He struck out 269 batters the following season and climbed even higher to 274 while winning the Cy Young in 1970. He averaged 20.0 wins per season during this five-year stretch with an ERA of 2.35.

Postseason Success

Gibson only got to compete in three postseasons, but he made the most of those opportunities. He was the MVP of both the 1964 and 1967 World Series. He would have been the MVP in 1968, too, if the Cardinals had won that one.

He made a total of nine starts in those three series, pitching a complete game in eight of the nine outings. He went 7-2 with a 1.89 ERA, a 10.22 K/9 and a K/BB ratio of 5.41. Hell, the man even hit two home runs. If Gibson isn't in your top five greatest postseason pitchers of all time, you're doing it wrong.

9. Greg Maddux (1986-2008)

Career Stats: 355-227, 5008.1 IP, 3.16 ERA, 6.06 K/9, 3.37 K/BB, 116.7 WAR

Five-Year Peak: 1993-97

During an era when baseballs were practically dripping with steroids, Greg Maddux repeatedly made opposing batters look helpless.

If we expand this five-year peak to the full seven-season surge from 1992 to 1998, Maddux had a pristine ERA of 2.15 and a WHIP of 0.97. He was never king of the strikeouts, but his rates of both walks and home runs allowed were absurd. His FanGraphs WAR during those seven years was more than 22 percent higher than the closest pitchers, Roger Clemens, Kevin Brown and Randy Johnson—each of whom had an ERA north of 3.00.

His first two and final six seasons were not great, but those middle 15 years cemented Maddux as one of the greatest painters to ever step on a pitcher's mound.

Postseason Success

A testament to his value added during the regular season, Maddux pitched in 13 postseasons during his 23-year career. There were a few serious duds along the way, but he went 11-14 with a 3.27 ERA in 198.0 innings pitched. For the most part, those losses were a product of dreadful run support or poor fielding, as he allowed 25 unearned runs in the playoffs and only gave up more than four earned runs in three of 30 starts.

His best multi-postseason run came in the latter half of the 1990s, starting with the 1995 World Series title. Maddux went at least 7.0 innings in all five of his starts in that postseason, including a complete game with no earned runs allowed in the World Series opener against the Cleveland Indians. From 1995 through 1999, he had a postseason ERA of 2.15 and an opposing slugging percentage of 0.321.

8. Roger Clemens (1984-2007)

Career Stats: 354-184, 4916.2 IP, 3.12 ERA, 8.55 K/9, 2.96 K/BB, 133.7 WAR

Five-Year Peak: 1986-90

Fair or not, Roger Clemens' career—just like Barry Bonds'—will forever be linked to steroids. At any rate, that's the only reason the all-time pitching leader in FanGraphs WAR is not in the Hall of Fame, even though the accusations were never officially corroborated.

What we know for sure is Clemens was filthy on the mound. Like with Maddux, the five-year peak is more of a seven-year run from 1986 to 1992. During that time with the Boston Red Sox, Clemens had a 2.66 ERA with 32 complete-game shutouts and at least 208 strikeouts in each season.

He won the AL Cy Young in 1986, 1987 and 1991 and was the runner-up in 1990—despite a 21-6 record with a 1.93 ERA. Clemens was also named the AL MVP in 1986. His FanGraphs WAR during this time was 54. No one else even reached 34.

Well outside that peak run, Clemens also won the Cy Young in 1997 and 1998 with the Toronto Blue Jays, in 2001 with the New York Yankees and in 2004 with the Houston Astros. It's incredible that he had a 2.48 ERA in 1986 and was even better at 1.87 two decades later in 2005.

Postseason Success

Though Clemens was great during the regular season, one of the biggest reasons he ranks outside the top three on this list is he wasn't that good when it mattered most.

There are noteworthy exceptions to that. En route to his second World Series ring, Clemens started Game 4 of the 2000 ALCS and Game 2 of the World Series, logging 17 shutout innings with just three hits allowed and 24 strikeouts. In all, 19 of his 35 postseason starts were quality starts—at least six innings with three or fewer earned runs allowed.

However, his career postseason ERA sits at 3.75, and in 12 trips to the playoffs, he only once posted an ERA of 3.20 or better (2.36 in 2001).

7. Clayton Kershaw (2008-Present)

Career Stats (through 2017): 144-64, 1935.0 IP, 2.36 ERA, 9.86 K/9, 4.18 K/BB, 58.0 WAR

Five-Year Peak: 2011-15

With all due respect to Justin Verlander, Felix Hernandez, CC Sabathia, Roy Halladay, Zack Greinke and the other great pitchers of this century, Clayton Kershaw was the only active or recently retired player who was a serious candidate for this list.

Given how extraordinary this left-hander has been, though, might No. 7 on the all-time list be a little too low?

From 2011 through 2017, Kershaw had a cumulative ERA of 2.10. He led the majors in ERA in each year from 2011 through 2014, and he was just 0.06 points behind Corey Kluber for last year's crown. Kershaw didn't pitch enough innings to qualify for the 2016 title, but his 1.69 mark would have been best by a long shot. He averaged an absurd 5.73 strikeouts per walk during those seven seasons.

Basically, the man has had no equal. He realistically could have won the NL Cy Young in each of the last seven years, but the voters decided to limit him to three trophies and four other top-five finishes. He also won NL MVP in 2014 with a 21-3 record and a 1.77 ERA.

Postseason Success

Just like Clemens, Kershaw has made a habit of wilting in October.

His strikeout numbers remain remarkable (10.25 per nine, 3.75 per walk), but his ERA balloons two full points to 4.35. That's largely because he can't seem to keep the ball in the yard, giving up 1.33 home runs per nine innings compared to 0.60 during the regular season.

Kershaw does have four career playoff starts with at least (exactly) seven innings pitched, three hits or fewer and one run or fewer allowed. However, he has also given up at least five earned runs in five of 19 games started, including a dud in Game 5 of the 2017 World Series. If he expects to truly be remembered as one of the greatest of all time, he needs to change that narrative soon.

6. Sandy Koufax (1955-1966)

Career Stats: 165-87, 2324.1 IP, 2.76 ERA, 9.28 K/9, 2.94 K/BB, 54.5 WAR

Five-Year Peak: 1962-66

Whereas most of these pitchers tapered off in a big way over their final few seasons, Sandy Koufax saved his best for last. The lefty was good from the outset, hurling a pair of complete-game shutouts in just five contests started in his first season as a 19-year-old. But he was almost untouchable in his final four seasons.

Despite pitching through pain and arthritis that ended his career after 12 years, Koufax boasted a minuscule 1.86 cumulative ERA from 1963 to 1966. He averaged 24.3 wins and 307 strikeouts per year in that stretch, including 382 strikeouts in 1965. He won both the NL MVP and Cy Young in 1963 and proceeded to win the Cy Young again in 1965 and 1966.

Koufax is to baseball what Barry Sanders was to football, abruptly retiring while still on top of the world and leaving us to wonder if two or three more healthy seasons might have been enough to make him the undisputed greatest ever.

Postseason Success

Regular-season Koufax was great, but postseason Koufax was the Greek god of the rubber.

In 57.0 innings across four postseasons, he gave up a grand total of six earned runs for an ERA of 0.95. He only allowed multiple earned runs in one of his eight appearances, and he struck out 15 Yankees in that 5-2 victory in the 1963 World Series. Two years later, Koufax hurled complete-game shutouts in Games 5 and 7 against the Minnesota Twins. He was, not surprisingly, the MVP of both of those series.

Koufax issued two walks and recorded two strikeouts in his lone appearance in the 1966 World Series. Before that final game, he had 59 strikeouts against just nine walks (6.56 K/BB) in his postseason career.

5. Pedro Martinez (1992-2009)

Career Stats: 219-100, 2827.1 IP, 2.93 ERA, 10.04 K/9, 4.15 K/BB, 84.5 WAR

Five-Year Peak: 1997-2001

Like several others in the top 10, Pedro Martinez had a peak that was really a seven-year stretch of dominance, extending from 1997 to 2003. Most of that run came with the Boston Red Sox, but he got it started with the Montreal Expos.

Martinez hurled 13 complete games with a 1.90 ERA and 305 strikeouts in 1997, winning the NL Cy Young almost unanimously. In both 1999 and 2000, he was the unanimous winner of the AL Cy Young Award. He also finished top three in the voting in 1998, 2002 and 2003. A rotator cuff injury limited him to 18 starts in 2001, keeping him out of that Cy Young race. But he still struck out 163 batters in 116.2 innings that year.

Martinez averaged 11.26 strikeouts per nine innings and 5.59 strikeouts per walk with a 2.20 ERA during those seven years.

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Postseason Success

Martinez pitched 17 scoreless innings in the 1999 postseason. In his other 13 career playoff appearances, though, he had an ERA of 4.19 and wasn't nearly as lethal in the strikeout department (73 in 79.1 innings) as he was during the regular season.

It'd be one thing if those playoff stints came outside his most dominant years, but more than 80 percent of his career postseason games came in the 1998-2004 window.

Despite the infamous eighth-inning meltdown in Game 7 of the 2003 ALCS, it wasn't all bad. Martinez went at least six innings in 13 of his 16 postseason appearances, including seven shutout innings in Game 3 of the 2004 World Series. He was a solid postseason pitcher. He just wasn't as great as he was from April through September.

4. Cy Young (1890-1911)

Career Stats: 511-316, 7354.2 IP, 2.63 ERA, 3.43 K/9, 2.30 K/BB, 131.5 WAR

Five-Year Peak: 1901-05

Trying to compare Cy Young's numbers to today's baseball is an exercise in futility. Just during this five-year stretch, he pitched 184 complete games with a 1.93 ERA. Clemens had 118 complete games in his 24-year career, and he has thrown more complete games than anyone dating back to 1984.

The wild thing is this was par for the course back then. From 1901 to 1905, 34 pitchers logged at least 100 complete games. Young didn't even throw the most innings during this time (Joe McGinnity did), and he only led the AL in ERA in one of the five seasons (1901).

As a result, his peak WAR was never as high as those of the others in our top 10, even though someone posting the same numbers in 2018 would get all of the wins above replacement. He did have a WAR of at least 5.6 in 18 consecutive seasons, though, which is even more impressive than a handful of seasons of being worth at least nine wins above the league average.

Postseason Success

Because the World Series wasn't a thing until 1903, Young didn't get much of a chance to compete in the postseason. But he did pitch a ton for the Boston Americans in that first series. He threw nine innings each in Games 1, 5 and 7 and came on in relief for seven frames in Game 3. In all, he pitched 34 innings with a 1.85 ERA.

In non-postseason news, the main reason the winningest pitcher in baseball history and the namesake for the sport's most prestigious pitching award only ranks fourth on our list is a lack of strikeouts. Young pitched an incomprehensible number of innings, but swings and misses were few and far between. In 1893, Young walked 103 batters and struck out 102 in 422.2 innings.

3. Randy Johnson (1988-2009)

Career Stats: 303-166, 4135.1 IP, 3.29 ERA, 10.61 K/9, 3.25 K/BB, 110.6 WAR

Five-Year Peak: 1998-2002

Flamethrowers aren't supposed to get better with age, but Randy Johnson in his late 30s was quite the exception to that rule.

The Big Unit won 100 games from 1998 to 2002 between Seattle, Houston and Arizona. The brief stop in Houston was the most ridiculous, as he went 10-1 in 11 starts with four shutouts and a 1.28 ERA. He actually got a couple of votes for the 1998 NL Cy Young, even though he was only with the Astros for two months. He did win the Cy Young in each of the next four seasons with the Diamondbacks. During those five years, he had a 2.63 ERA.

The unreal numbers were the strikeouts, though. Johnson fanned at least 329 batters in five straight seasons. In the last four decades, a pitcher has struck out at least 320 batters in a season five times, and Johnson accomplished all of them. Consecutively. His K/9 during this half decade was 12.33.

Postseason Success

From the 1995 ALCS through the 2001 NLDS, Johnson lost seven consecutive postseason starts, compiling a 4.26 ERA in the process. The final three starts of his postseason career were even worse, as he allowed 15 earned runs in 14.2 innings with a mere 10 strikeouts.

But Johnson's five appearances in the 2001 NLCS and World Series were enough to make him a postseason legend.

He got the win in all five of those contests, including a pair of complete-game shutouts. His combined pitching line in those series was 33.1 innings, 19 hits, four earned runs, six walks, 38 strikeouts, a 1.08 ERA and a 0.75 WHIP. Though it's a series that will forever be remembered for Luis Gonzalez's title-winning hit off Mariano Rivera, Johnson and Curt Schilling were named the 2001 World Series co-MVPs.

2. Walter Johnson (1907-1927)

Career Stats: 417-279, 5914.2 IP, 2.17 ERA, 5.34 K/9, 2.58 K/BB, 117.1 WAR

Five-Year Peak: 1910-14

The beauty of Walter Johnson's career is you can point to any five-year stretch from 1907 through 1919 and be mighty impressed. During those 13 seasons, he only twice posted an ERA above 1.90, and it was never higher than 2.22.

His final eight seasons put a damper on most of his efficiency numbers, but through 1919, he had 297 wins with a 1.65 ERA, a 0.97 WHIP and 5.75 strikeouts per nine innings. Compared to today's game, that strikeout rate isn't impressive. Back then, though, the Big Train led the AL in total strikeouts in 12 out of 15 seasons.

Forced to pick one five-year peak, though, we're going with the first half of the 1910s. Johnson averaged 29.4 wins per season with a 1.50 ERA thanks in large part to 41 of his record-setting 110 career shutouts.

1913, in particular, was preposterous. He went 36-7 with a 1.14 ERA and 11 shutouts. Johnson struck out 1,291 batters from 1910 to 1914, which is 467 more than any other pitcher could boast during that time.

Postseason Success

In spite of Johnson's dominance, the Washington Senators were not good enough to reach the postseason until late in his career. But even at 36 years old, he still had more than enough gas left to hurl a few complete games.

Johnson appeared in six contests (five starts) between the 1924 and 1925 World Series. In all five of his starts, he went the distance, including a 12-inning loss in his first postseason appearance. In all, he pitched 50 innings with a 2.52 ERA, and he was on the mound when the Senators won the 1924 World Series.

1. Christy Mathewson (1900-1916)

Career Stats: 373-188, 4780.2 IP, 2.13 ERA, 4.71 K/9, 2.96 K/BB, 90.0 WAR

Five-Year Peak: 1907-11

Christy Mathewson's career was a few years shorter than each of the other players in our top four, which is why his cumulative WAR isn't quite as high as the likes of Young, Randy Johnson and Walter Johnson. It's amazing what he was able to accomplish in his 14 full and three partial years, though.

Mathewson's best individual season actually came two years before the start of his multiyear peak. In 1905, he won 31 games with a 1.28 ERA, leading the National League in strikeouts for the third consecutive season. And as we'll get into shortly, he had one heck of a showing in that World Series.

From 1907 through 1911, though, he won 139 games (27.8 per year) with a 1.69 ERA and 0.96 WHIP. He averaged 6.8 shutouts per season and even picked up 12 of his 30 career saves during this time. And while his K/9 rate doesn't compare to the more recent pitchers, Mathewson's K/BB ratio (3.98) was rock solid and significantly better than those of other legends of this era, like Johnson, Young and Grover "Pete" Alexander.

Postseason Success

Mathewson's numbers were strong across the board, but the postseason factor made him the No. 1 pitcher no matter how many ways the formulas were tweaked. It's all but impossible for anyone to ever be more dominant than he was in 1905, pitching complete-game shutouts in Games 1, 3 and 5 of the World Series to pace the New York Giants to a championship.

He was no one-hit wonder, either. Mathewson made eight more starts in the 1911-13 World Series. He only gave up more than two earned runs in one of those games, despite pitching more than nine innings in four of them.

In all, he pitched 101.2 innings with a 0.97 ERA and four shutouts. He only managed a 5-5 record, though, as the Giants gave him virtually no run support in the process of losing three straight World Series.

Advanced statistics courtesy of FanGraphs and Baseball Reference.

Kerry Miller is a multi-sport writer for Bleacher Report. You can follow him on Twitter, @kerrancejames.