Mulciber (first name unknown) attended Hogwarts School of Witchcraft and Wizardry, where he was sorted into Slytherin House alongside Avery and Severus Snape. Mulciber and Avery seem to have had a particular reputation for cruelty, greater even than many of those with whom they were friends (a group who according to Bartemius Crouch Jr/Mad-Eye Moody "nearly all turned out to be Death Eaters").
According to Igor Karkaroff's evidence, Mulciber specialised in the Imperius Curse, forcing "countless people to do horrific things". After Voldemort's downfall, Mulciber was imprisoned in Azkaban, which he escaped during the mass breakout of 1996. He was among the Death Eaters sent by Voldemort to fetch the prophecy concerning Harry Potter from the Department of Mysteries and fought in the ensuing battle between the Death Eaters and the Order of the Phoenix.
Re-imprisoned in Azkaban, Mulciber escaped again in 1997. It is not known whether he fought at the Battle of Hogwarts (though it may be likely), nor is it known what happened to him afterwards (whether he was killed or imprisoned, or is now 'on the loose')