Jack Sharkey (Lithuanian: Juozas Povilas Žukauskas, October 26, 1902 – August 17, 1994) was an American world heavyweight boxing champion. He was born Joseph Paul Zukauskas (his birth surname is sometimes given as Cukoschay), the son of Lithuanian immigrants, in Binghamton, New York, but moved to Boston, Massachusetts as a young man. Sources report little of his early life until, at the outset of World War I, teenaged Joseph repeatedly tried to enlist in the Navy. Turned down because of his age, he was not able to enlist until after the end of the war.
It was during his tenure in the Navy that he first showed interest in boxing. Tall and husky for a man of his generation, Joseph was encouraged by his friends in the service to box. He quickly established notoriety as the best boxer aboard any vessel on which he served. During his brief returns home to Boston he took part in his first fights for pay, the first on January 24, 1924, against one Billy Muldoon, whom he knocked out in the first round. By the time of his honorable discharge just short of a month later, he had won a second fight and was already earning write-ups in the Boston papers.