Death

Death is the ruler of the Land of the Dead in the episode "Death in Bloom". He plays the drums in a competition against Finn. He almost kills Finn, but then Finn brings up Peppermint Butler and Death gives back Jake's memory and the life of Princess Bubblegum's plant. He is shown to have various powers, such as the "Kiss of Death", encasing people in forcefields, and sending people back to the Land of Ooo.

Trivia

 * In certain religious views, death is referred to as the Grim Reaper, or the Angel of Death. He is the one who causes the death of victims and sends them to the afterlife. His traditional appearance is a skeletal figure carrying a large scythe, and is clothed in a black cloak with a hood. The very touch of death will instantly cause his victims to die.
 * For some reason, his head is a horse skull, unlike a usual human skull head.
 * Death was originally going to be some sort of Japanese cosmic alien, according to Jesse Moynihan's blog.
 * When Death said "I"ll see you guys later" to Finn and Jake, he probably meant when they die and are sent to the land of the dead.
 * Death's appearance as a farmer is likely a sublime reference to his trademark item, a scythe, is a piece of farming equipment.
 * Oddly enough, Death does not look like what the Grim Reaper (Death) usually looks like. Not A farmer, but A Skeleton in A Black Rob weilding A Scythe.