Nerull
Nerull is a greater god of Death. He shares a lot of similarities with the Grim Reaper (death motif, know as "the reaper", scythe, ect...). He hates life. He got usurped by the Raven Queen in Points of Light.
In Greyhawk he hangs out on Agathys, the icy sixth layer of Carceri. Here he maintains a citadel where his priests perform necromantic experiments and rituals. They are always looking for new subjects to test on, so it is advised to stay clear of the Necromanteion without good reason. Or even with good reason. Or getting anywhere near Agathys. In fact, it's best not to go to Carceri ever.