Eric Williams was considered the black sheep of the Williams family and grew up to be a gambler and professional criminal, eventually becoming a member of the Maggia. When his younger brother Simon (as Wonder Man) supposedly died at the hands of the Avengers, Eric swore revenge on them.
With contacts from the Maggia, he hires the Tinkerer for his plot and he builds on his right arm a scythe which can cut through almost anything and can fire energy blasts and electricity shocks. The scythe also contained a device created by Ultron that could put any person into a coma.
Eric then takes the pseudonym Grim Reaper and nearly defeats the Avengers on his first outing, but was defeated by the Black Panther. He then forms the Lethal Legion with the likes of the Living Laser, Man-Ape, and the Swordsman and the group fought the Avengers, but they were defeated by the Vision. The Grim Reaper has remained a constant threat to the Avengers ever since.