Wizard, Death Eater, and Ministry of Magic employee, Augustus Rookwood was accused of spying for Lord Voldemort during the First War and was subsequently imprisoned in Azkaban after Death Eater Igor Karkaroff's testimony. Rookwood worked in the Department of Mysteries, passing sensitive information via what Karkaroff claimed was a network of well-placed wizards both inside and outside the Ministry.
Rookwood escaped from Azkaban in 1996 during the mass breakout, at which time he returned to his role as a Death Eater. He was among the group of Death Eaters with whom Harry and his friends battled at the Department of Mysteries and was also present at the Battle of Hogwarts. It is possible that Rookwood was responsible for the explosion that killed Fred Weasley, given that Percy Weasley shouted Rookwood's name whilst chasing him just prior to that explosion.