| Billy Mullen | |
| Bats: | Right |
| Throws: | Right |
| Birth Date: | 23 January 1896 |
| Birth Place: | St. Louis, Missouri |
| Death Place: | St. Louis, Missouri |
| Debutleague: | MLB |
| Debutdate: | October 2 |
| Debutyear: | 1920 |
| Debutteam: | St. Louis Browns |
| Finalleague: | MLB |
| Finaldate: | June 5 |
| Finalyear: | 1928 |
| Finalteam: | St. Louis Browns |
| Statleague: | MLB |
| Stat1label: | Batting average |
| Stat1value: | .220 |
| Stat2label: | Home runs |
| Stat2value: | 0 |
| Stat3label: | Runs batted in |
| Stat3value: | 2 |
| Teams: |
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William John Mullen (January 23, 1896 in St. Louis, Missouri – May 4, 1971) was a professional baseball player who played third base from 1920 to 1928.
Bill Mullen is survived by his daughter, June Mitchell, and her three sons, Tom, Robert, and Terry Mitchell. Tom owned a jazz restaurant in Cocoa Beach, Florida for some time until 2008, and now works for Kennedy Space Center. Also survived by his daughter, Dorothy Murray, and her three children, the late Linda Best (Murray), William Murray of Kirkwood, Mo. and Kim Higgins (Murray), Sappington, Missouri.