First appeared in Savage Tales #1 in 1971 and was created by Roy Thomas, Gerry Conway, and Gray Morrow. Dr. Ted Sallis became Man-Thing after injecting himself with a serum before crashing his car into a swamp with magical energy.
This is going off the debut of comic book characters. In the cases of characters who were introduced in other media originally and added to the comics canon later along (ex: Harley Quinn) it'll go by actual debut year.
