The pitcher that struck out the most batters in history is Nolan Ryan. He has struck out 5,714 batters during his career from September 11, 1966 until September 22, 1993.
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Roger Clemens
nolan ryan
Josh Beckett
Well in more recent times as of post-1900s, Nolan Ryan struck out 383 batters in 1973 season with the California Angels. Hope that helps.
Nolan Ryan struck out the most batters, but Reggie Jackson struck out the most at the plate.
Koufax
There have been 51 instances in which a pitcher has struck out four batters in one half inning. The most recent was Scott Shields of the Los Angeles Angels on June 21, 2008.
As of the 2008 season, that is Ferguson Jenkins who struck out 274 batters in 1970.
Arguably the best MLB pitcher of all time was Nolan Ryan. While he had thousands of walks, he also had a relatively low ERA and struck out over 5,000 batters.