Harry Edwin Heilmann (August 3, 1894 – July 9, 1951), nicknamed "Slug", was an American baseball player and radio announcer. He played professional baseball for 19 years between 1913 and 1932, including 17 seasons in Major League Baseball with the Detroit Tigers (1914, 1916–1929) and Cincinnati Reds (1930, 1932). He was a play-by-play announcer for the Tigers for 17 years from 1934 to 1950.

Heilmann won four American League batting championships, securing the honors in 1921, 1923, 1925 and 1927. He appeared in 2,147 major league games, including 1,525 games as a right fielder and 448 as a first baseman and compiled a career batting average of .342, the 12th highest in major league history, and third highest among right-handed batters. At the time of his retirement in 1932, Heilmann ranked sixth in major league history with 542 doubles and eighth with 1,543 RBIs. He remains one of only six players in American League history to hit .400 for a season, having accomplished the feat in 1923 with a .403 batting average. He also hit .394 in 1921. At his peak from 1921 to 1927, Heilmann compiled a .380 batting average, .452 on-base percentage, .583 slugging percentage, and averaged 116 RBI, 41 doubles, 11 triples, and 104 runs scored per season. From 1919 through 1930, Heilmann hit over .300 for 12 consecutive seasons. He also compiled six 5-hit games and 49 4-hit games in his 17-year major league career.

After retiring from baseball, Heilmann ran unsuccessfully for the office of Detroit City Treasurer and operated a semipro baseball team in 1933 and, in 1934, began a career as a radio broadcaster. From 1934 to 1942, he was play-by-play announcer for the Tigers on station WXYZ and the Michigan Radio Network, covering parts of Michigan located outside metropolitan Detroit, while rival Ty Tyson called games for station WWJ in Detroit exclusively. From 1943 to 1950, Heilmann was the exclusive radio voice of the Tigers throughout the state. Heilmann died from lung cancer in July 1951; he was posthumously elected to the Baseball Hall of Fame six months later in January 1952 after garnering 86.75% of the votes.

Heilmann was born in San Francisco in 1894. His father, Richard W. Heilmann, was born in 1860 at Sacramento, California, the son of an Irish mother and a father from Saxony. His mother, Mary (McVoy) Heilmann, sometimes referred to as Mollie, was born in 1864 in County Roscommon, Ireland. Harry was the couple's fourth surviving child, having an older sister, May, and two older brothers, Richard Jr., and Walter. Heilmann's father operated a soap business, ran as a Republican for the office of Supervisor of San Francisco's Ninth Ward in 1896, and died in June 1897 at age 36. As a boy in the 1890s and continuing at least through the time of the 1900 Census, Heilmann lived with his family at 708A Brannan Street in what is now the South of Market district of San Francisco.

Heilmann's older brother, Walter, was a gifted athlete who attended Sacred Heart Cathedral Preparatory (then "Sacred Heart College") in San Francisco. On June 3, 1908, a year after the city's devastation by earthquake, Walter died at age 16 while on a sailboat excursion with three schoolmates to visit the battleship USS Connecticut in drydock at the Hunters Point Naval Shipyard, near the present site of Candlestick Park. The boat capsized in a squall, and Walter drowned while trying to swim to shore; the other three boys were rescued.

As of 1910, Heilmann was living with his mother at 112 Sixteenth Street in the Dogpatch neighborhood of San Francisco. Heilmann followed his older brother to what is now Sacred Heart Cathedral Preparatory, where he played baseball, track and field, and basketball. He graduated from Sacred Heart in 1912 at age 17 with a collegiate certificate. After graduating from Sacred Heart, Heilmann worked as a bookkeeper for the Mutual Biscuit Company.

Heilmann appeared in a semipro baseball game in 1913 for a team from Hanford, California. While playing for Hanford, he was signed by a scout for the Portland Beavers of the Pacific Coast League (PCL). After being signed by the Beavers, Heilmann was assigned to the Portland Colts of the Northwestern League. He compiled a .305 batting average in 122 games for the Colts.

In September 1913, Heilmann was drafted by the Detroit Tigers. He made his major league debut with the Tigers on May 16, 1914, and played in 68 games that year, batting .225 and committing six errors in 31 games in the outfield (29 games in center field) for an .870 fielding percentage.