The Lernean Hydra is a monster of Greek mythology, which fought Hercules. The Marvel adaptation was created in 1985 by John Buscema and Roy Thomas. Making its first appearance in issue #356 of the 1st volume of the Thor comic book series.
Background
The Lernean Hydra is a descendant of Set, an Old One. It was sired by Set's granddaughter Echidna who mated with Typhon, one of the Titans. A multi-headed dragon-like monster with serpentine heads whose blood is venomous and can regenerate its heads, two growing to replace one. It was one of the "labors" assigned to the heroic demigod Hercules.