Herbert Ehler Thormahlen aka Lefty (July 5, 1896 – February 6, 1955) was a pitcher in Major League Baseball who played from 1917 through 1925 for the New York Yankees (1917–20), Boston Red Sox (1921) and Brooklyn Robins (1925).

Listed at 6 ft 0 in (1.83 m), 180 lb., Thormahlen batted and threw left-handed.

When he was 21 years old, he made a one-game appearance for the New York Yankees in 1917 before returning to the minor leagues in 1918.

In a six-season major league career, Thormahlen posted a 29–28 record with 148 strikeouts and a 3.33 ERA in 104 appearances, including 64 starts, 27 complete games, four shutouts, three saves, and 565 innings of work.

Thormahlen died in Los Angeles at age of 58.