Mark David McGwire (born October 1, 1963), nicknamed Big Mac, is an American former professional baseball first baseman. His Major League Baseball (MLB) playing career spanned from 1986 to 2001 while playing for the Oakland Athletics and the St. Louis Cardinals, winning one World Series championship each, with Oakland as a player in 1989 and with St. Louis as a coach in 2011. One of the most prolific home run hitters in baseball history, McGwire holds the major league career record for at bats per home run ratio (10.6), and is the former record holder for both home runs in a single season (70 in 1998) and home runs hit by a rookie (49 in 1987).