Zanthar

A dark purple-furred cube-shaped headless gorilla-like creature that walks on all four of its arms. He has a light-purple patch much like a loaf of sliced bread and small trees growing out of his back and shoulders. He also wears a party hat. In "Weirdmageddon Part 1", Bill refers to him as "the Being Whose Name Must Never Be Said" before referring to him by his real name.