Dungeons & Dragons is really to blame. There be Ett in the game from the start!
According to 5e cosmology, the D&D demon lord Demogorgon apparently turned orcs into giant mockeries of the twin-headed Prince of Demons and that's how ettins were born.
Here are some more examples. I'm sure there are others I'm forg-ettin'.
Amanda Visell's Ice God:
Two-headed Monster from Sesame Street
Harryhausen's stopmotion monster:
Abomination from The Thing With Two Heads:
Two Headed Monster from Adventure Time:
Jenny from Big Guy and Rusty the Boy Robot:
Designer toy Yakonimonz by Tanin Tumth of #MOK :
Designer toy Cyco Ape by Mishka:
And sometimes they got three heads, 'stead of two. What's that called? My suggestion: "threttin".