Emmett Jerome "Heinie" Mueller (July 20, 1912 – October 3, 1986) was a Major League Baseball player for the Philadelphia Phillies from 1938 to 1941.

Amazingly, in the very same game, Ernie Koy, from the opposing Brooklyn Dodgers, also hit a home run in his very first Major League at-bat.

This game remains one of only two in Major League history in which multiple players hit home runs in their first ever at-bat (the other occurring on August 13, 2016, when teammates Tyler Austin and Aaron Judge hit their home runs in consecutive debut at-bats).

Interestingly, the first Major League ballplayer ever to hit a home run on the very first pitch in their first at bat is named Walter Mueller; it is unclear whether the two ballplayers are related, although coincidentally, Walter did have a brother, also named Heinie Mueller, who himself played in the Major Leagues.

Having missed four seasons to military service, Mueller did not make the cut and was released by the Phillies on April 22, 1946.