The Grim Reaper, a scythe-wielding skeleton in a black hooded robe, is called Grim by most people. He is over 137,000 years old, and speaks in a Jamaican accent. He was elected to his position as the Grim Reaper when he was in middle school. His scythe is the source of his powers and possesses many magical qualities; although he is still capable of using magic without it, these instances are rare.
Grim met Billy and Mandy when he went to reap Mr. Snuggles. But Mandy neglected. Then she challenged Grim to a bet. If she and Billy lose then Grim can take Mr. Snuggles and if they win, Mr. Snuggles will live and Grim will be their best friend forever. The challenge was Limbo, which Grim's choice, in the Limbo Realm. But Mandy cheated by using Mr. Snuggles' unusual trick.
By losing the Limbo contest to Billy and Mandy, Grim is fated to be their "best friend" forever. They treat him like a slave, though Billy is more friendly towards him and seems to admire him (although Grim is usually most annoyed by him). He is often forced to do their chores and create supernatural fun for them. Grim enjoys all kinds of chaos, despair, torture, and many other dark things. Grim is adapting to modern life, and is usually seen, in his free time, watching television, mainly horror movies or soap operas. He also has a bottomless trunk where all types of dark objects are found; Billy usually abuses them, creating chaos and destruction.
- In the comic book, Grim Tale's, Mandy became Grim's wife and appears to be Jack Skellington's relative.