The comic strip known today as Popeye began in 1919 under the name Thimble Theatre. The character of Popeye wasn’t a member of the original cast, which included Olive Oyl, her brother Castor Oyl, and Olive’s boyfriend Ham Gravy; all of those characters are in the Public Domain. Popeye the Sailor, however, was introduced in January 1929, and should have joined them at the end of 1985.
He was supposed to be a temporary character, part of a storyline in which Ham and Castor hire him as part of a get-rich scheme. He was apparently killed off at the end of the story, but readers like him, so he got better.
Not only did Popeye take over Thimble Theatre, he quickly became a pop culture hit. Fleischer Studios started producing animated shorts in 1932, and he was the star of a radio series in the mid 1930s. He has since appeared in comic books, original-for-TV animated stories, and a love-it/hate-it live-action film starring Robin Williams.
Another copyright-related wrinkle to the Popeye story involves his nemesis Bluto. Or is it Brutus? When production of the TV shorts began, they producers thought that they didn’t have the rights to use Popeye’s barrel-chested rival Bluto (thinking that he had been created for the theatrical shorts), so they created an essentially identical character with his chest lowered to his belly, and called him “Brutus”. In fact, Bluto originated in the comic strip, so Brutus was just as available for the TV cartoons as Olive Oyl and Swee’pea.