Death

Death is one of the horsemen of the apocalypse, in the game it is referred to as the "Fourth seal broken by Notch". When it appears, it will stride around killing random mobs. Its horse is skeletal. When it finishes the reaping, it will sprint torwards the nearest Darkness Stable. Like all of the horsemen, it is invincible.

Grim Reaper's Encyclopedia Entry
If you live it, I will come.

Trivia
Its GRE Entry is a reference to the Field of Dreams quote "If you build it, they will come".