Tom Marvolo Riddle (more commonly known as You-Know-Who, He-Who-Must-Not-Be-Named, or Lord Voldemort) is a half-blood wizard who made several horcruxes due to murdering. He started an army of dark wizards and witches named the Death Eaters. Tom was known to maim, tortue, interrigate and murder anyone who opposes him. He was once a master of the Elder Wand until death by Harry Potter. He murdered his own Filthy Muggle Grandfather and father because of muggle relationship, he blamed the crime on his uncle Gaunt and he was sent to Azkaban.
Voldemort was leader of the death eaters starting in the 70's and ending in 1998. The death eaters were his faithful servants.