5. Cy Young

By the time Denton True "Cy" Young joined the upstart Boston Americans for their inaugural 1901 season, he was already a legend with 267 wins to his name. Many expected the 34-year-old to be in the twilight of his career, but "The Cyclone" instead authored a second act that defined the birth of modern baseball. In his first year in Boston, he secured the American League’s first Pitching Triple Crown, leading the league in Wins (33), ERA (1.62), and Strikeouts (158).

Young’s dominance in the early 1900s was a clinic in efficiency. He followed his Triple Crown with back-to-back seasons leading the AL in Wins (32 in 1902 and 28 in 1903). His 1903 campaign was a masterpiece, as he famously threw the first pitch in modern World Series history and earned two wins to lead Boston to the inaugural championship. His control was so precise that he led the AL in WHIP and Strikeout-to-Walk ratio nearly every year, proving that velocity was nothing without his signature "cyclone" precision.

On May 5, 1904, Young achieved a feat of such advanced quality that remains one of the greatest single-game performances in history: the first perfect game in American League history. Out-dueling the eccentric Rube Waddell, Young retired all 27 Philadelphia Athletics in just 83 minutes. This was part of a staggering stretch where he didn't allow a hit for 24 consecutive innings, a record that stood as a testament to his untouchable command during the Deadball Era.

Young remained a workhorse for Boston through 1908, remarkably recording three more 20-win seasons as he pushed past the age of 40. Before being traded to Cleveland in 1909, he amassed 192 wins in a Boston uniform—a franchise record he currently shares with Roger Clemens. He finished his Boston tenure with a microscopic 2.00 ERA, 1,341 strikeouts, and a 0.970 WHIP, figures that set an impossible bar for every Red Sox pitcher who followed.

Inducted into the Baseball Hall of Fame in 1937 as part of its second class, Young was later honored as a charter member of the Boston Red Sox Hall of Fame. As for this high rank, it is a testament to how good he was, even though eight of his legendary 22 seasons were in Boston.