That would depend on when one believes the 'modern era' of MLB began. For this answer, we will take Baseball Almanac's year of 1977 as the beginning of the 'modern era'. Since 1977, the most wins in a season by a pitcher is 27 by Bob Welch of the Oakland Athletics in 1990.
Starting at 1920, that is Jim Bagby of the Cleveland Indians in 1920, Lefty Grove of the Philadelphia Athletics in 1931, and Denny McLain of the Detroit Tigers in 1968 with 31.
AL spalding 47
Al Spalding with 47 in 1876. In the modern era, Russ Ford with 26 in 1910. However, Pete Alexander won 28 in 1911.
he is the most famous and greatest basketball player in the world for gaining records for most points in a single season a triple double and most wins in 1 season that's 72 and has not been broken yet
In 1968, Detroit's Denny McLain recorded 31 wins; the most by any player since 1950. McLain was the last pitcher to reach 30 wins in a season.
The franchise record for wins in a season is 41 by Jack Chesbro in 1904.
Joe Wood with 34 wins in 1912.
Through the 2008 season, that is Hall of Famer Tom Seaver who had 25 wins in 1969.
Sandy Koufax (27 wins)
John Smoltz 24-8 (1996)
The Pirates franchise record for most wins by a pitcher in a season is held by Frank Killen who won 34 games in 1893.