Ekrizdis

Ekirzdis was an immensely evil wizard in the Harry Potter universe.

Biography
Ekirzdis was of unknown origin (possibly Greek though, given that early Dark Magic was practiced in ancient Greece, and given the sounding of his name) who roamed the world before settling in an ancient island in the stormy North Sea, East of Britain. The island had been left by the Ice Age and was all alone in the choppy sea, a perfect location for Ekirzdis' dark desires.

By unknown means, he lured Muggle sailors to his island, then would capture them, torture them with the Cruciatus Curse and other dark magics, and then he would finally kill them. All through no apparent reason other than an insatiable bloodlust and a possible insanity.

Ekirzdis died long before the novels began, but the Ministry found his Island, and entered it, finding the "least frightening" things inside were Dementors. It's unknown what was so scary the Ministry refused to speak of it, but its possible Ekirzdis made furniture out of his victims bones or other such gruesome acts, which is highly likely given he was insane.

Magical abilities

 * Cruciatus Curse: He could summon enough hatred to channel this rage-fuelled curse effectively.
 * Concealment charm: Ekirzdis made his entire Island home invisible and unchartable on a map, regardless of it being a Muggle or wizard map.