The Grim Reaper is a non-playable character in the game. When your Sims are ready to die, he will cast a spell and that Sim will die. He appeared in version 5.3.0.
The Grim Reaper will appear when your Senior Sim's Life Dream Duration Circle turns red. He will cast a spell to your Senior Sim; that sim will vanish and leave behind a Life Orb, then the Grim Reaper will vanish. The Grim Reaper will leave the house.
He visits your (Senior) Sims' house when they are in the last quarter of their life. Sometimes he can be found using your Sims objects, such as a Stereo, a Bookshelf, barbecues, ect.
The Grim Reaper wears a dark cloak with the hood up, showing no face and floats around.
Grim appears in the following quests: