Otto Charles "Pep" Deininger (October 10, 1877 – September 25, 1950) was a German center fielder in Major League Baseball who played for two different teams between 1902 and 1909. Listed at 5' 8+1⁄2", 180 lb., Deininger batted and threw left-handed. He was born in Wasseralfingen, Germany.
Deininger started his major league career in 1902 as a pitcher for the Boston Americans. He posted a 9.75 earned run average with two strikeouts and nine walks in two appearances, including one start, and did not have a decision. He later switched to the outfield, appearing in 56 games in parts of two seasons with the Philadelphia Phillies.
In a three-season career, Deininger posted a .263 batting average (46-for-175) with 16 runs batted in and 22 runs scored, including 10 doubles, one triple, and five stolen bases with no home runs.
Deininger died in Boston, Massachusetts, at age 72.