Joseph L. Greenstein (January 2, 1893 – October 8, 1977), better known as The Mighty Atom, was a 20th-century strongman known for highly unusual feats of strength and endurance.
Greenstein was born to a Jewish family in Suwałki, Poland, in 1893. As a child he suffered from respiratory ailments, and at age 14, a team of doctors predicted he would die from tuberculosis. Around that time, he became acquainted with a Russian circus strongman, Champion Volanko, who mentored Greenstein. Greenstein traveled with Volanko and the Issakoff Brothers Circus for eighteen months, learning the strongman's training regimen. After this, he returned to Poland and married his wife, Leah.
He began his career as a wrestler. However, due in part to rising anti-Semitism in Eastern Europe, he then left for the United States. He first went to Galveston, Texas, working as a dockworker and oil field worker. He also wrestled professionally at this time as Kid Greenstein. In 1914, The Houston Daily Post reported that a friend of Greenstein accidentally shot him in the middle of the forehead. The report states the bullet did not enter his skull, and "flattened out against his forehead". This experience sparked Greenstein's interest in the mental powers associated with strength, and he gradually developed an array of strongman feats.