John Sappo is the eponymous protagonist of E. C. Segar's comic strip Sappo (Originally The Five-Fifteen), which was the "topper", or complementary strip, to Segar's Popeye (Originally Thimble Theatre).

John Sappo is an everyman whose misadventures in everyday life (such as trying to catch the 5:15 train) dominated the series at first; however, after he took a tenant known as Professor O. G. Wotasnozzle, his adventures began to involve Wotasnozzle's daring inventions and experiments. Although usually annoyed by the Professor's schemes, Sappo would at times find himself going along, tempted by the prospect of riches and success, only to end up facing catastrophe.