Popeye's story and characterization vary depending on the medium. In his debut storyline, Popeye's superhumanly proportioned strength and endurance stemmed from the "luck" he acquired by rubbing the feathers of the head of Bernice, a "whiffle hen", thus enabling him to survive fifteen gunshot wounds. By the end of 1929, however, Popeye's strength had become a regularized fixture of his character, with spinach, by 1932, becoming the primary repository of his prowess.

Source: Wikipedia