Ummm...well, I'm sure not the guy who's gonna suck out your soul.
Hunson Abadeer (AKA "Marceline's Dad") is a demon on Adventure Time, the Lord of Evil and the Ruler of the Nightosphere, though he wants to retire and let Marceline take over. He usually appears as a blue-gray humanoid form with fangs, pointed ears, and yellow snake-eyes with red pupils, while wearing a somber business suit and red boots, but he can also assume a monstrous form with a head like a double pouch, a fanged vertical mouth, horns, tentacles and tendrils. Hunson has a bad tendency to want to suck out others' souls, yet he seems to be on good terms with characters such as Peppermint Butler, and recognizes Gunter as by far the most evil thing he has ever encountered.
Abadeer appeared as a shopkeeper during the "Nightoween" Halloween 2013 event in Peach Creek Commons, where a portal had apparently opened to the Nightosphere. (This portal strongly resembles the one leading to the Mystery Dungeon in Eternal Vistas.) There, in his humanoid form, Hunson, somewhat like Dracula in earlier Halloween events, sold the player Halloween-themed objects from Adventure Time.
Marceline and her father are voiced by Olivia Olson and Martin Olson, who are father and daughter in real life.