The Grim Reaper
Grim is over 137,000 years old (as his early childhood took place during the Stone Age) and speaks with a Jamaican accent. The continuity of how Grim got his reaper status and powers jumps around quite a few times and it is unknown which way he really got his powers. For example in The Spider Queen he was elected to his position as the Grim Reaper while he was in middle school; however, in A Grim Prophecy, it is shown that he was the Grim Reaper since his childhood with his parents forcing him to be the Reaper. 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 quite rare.
By losing a limbo contest to Billy and Mandy, Grim is fated to be their "best friend" forever. Unfortunately for the Reaper, the contract legally binds him to them, such that if he ever did leave, he would spend eternity in Underworld Jail (to his terror) as a result of it. Though Billy is friendly towards him, Mandy treats him dominantly, and this angers and irritates him to the point where he constantly fantasizes about killing both of them. However, there have been instances that show that he does indeed care for them. He is often forced to do their chores and create supernatural fun for them. Grim is slowly adapting to modern life, and is usually seen, in his free time, watching television, mainly horror movies or soap operas. His adaption to everyday life also leads him to neglect his duties, and eventually not even care about who uses his scythe seeing as how it is constantly stolen. He also has a bottomless trunk, where all types of dark objects are found; Billy usually abuses them, creating chaos and destruction.
His love-and-hate relationship with Billy and Mandy seems to vary from each-other. He seems to be more annoyed with Billy than Mandy, due to his stupidity. Although Billy abuses Grim's powers as much as Mandy, Billy treats Grim with much more fairness and kindness, resulting in Grim caring and liking Billy. In Mandy's case, although they both share the same cynical and misanthropic view of humanity, Grim tends to dislike her more than Billy due to her abuse, cruel and disrespectful actions towards him. While Grim fears Mandy (like all the other characters), he has the power to openly rebel against her when she becomes too obnoxious and abusive.