The Grim Reaper

"Once they took their last breath,

I'm the soul collector,

baby I'm Death!"

-Death (That's So Raven)

The Grim Reaper is the guardian of the Underworld who Raven visits in the YTP, That's So Raven. He has a daughter named Lillith, who is a ferocious demon. He also appears in the Halloween special.

Trivia
He is without a doubt the scariest character (besides Satan) in the Matt universe.