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.
In the minor leagues that was Ron Necciai of the 1952 Bristol Twins who struck out 27 batters in a no-hitter against the Welsh Miners in an Appalachian League game. In MLB that was Nolan Ryan of the 1973 California Angels who struck out 17 batters in a no hitter against the Detroit Tigers.
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.
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.