Typhoeus

Typhoeus, also simply referred to as the hundred-headed dragon, was a monstrous creature created by the primeval goddess Gaea to fight the Olympian pantheon early in its existence.

Description
The creature was said to be a dragon with a hundred heads. Some accounts further described its heads as all being on fire, that a thousand poisonous vipers protruded from its back, and that its body was larger than a mountain.

History
Following the Olympian pantheon's overthrowing of their predecessors the Greater Titans and their imprisonment in the plane of Carceri, their mother goddess Gaea sent monstrous creatures against the Olympians in order to liberate and avenge the Titans. According to some accounts, the Olympians first fought Typhoeus before having to do battle with the gigantes, whilst other accounts spoke of Typhoeus being Gaea's final creation sent against them. The creature was ultimately buried beneath a mountain, either by the gods collectively or by Zeus alone.