Erik Calutain, often named by his pseudonym "Blue Man", is a well-respected wizard in the Ministry of Magic, heading the Department of Investigations. He was responsible for the recent deposition of thirteen Aurors whom he deemed to be disloyal and a danger to the Ministry.
In his past, Calutain had well-known ties to Kali and the Kalite cause, and fought on Kali's side during the Auror War. In the aftermath of the Auror War, he redeemed himself in the eyes of then-Minister of Magic Archibold Herring, and earned a post at the Ministry. He has since been a model employee, widely regarded as one of the brightest individuals in the entire Ministry and a likely successor for James Karroll as Minister. His works have dealt mostly with rooting out corruption within the Ministry, and he has by most accounts greatly improved the efficiency of the Auror Department, Department of Mysteries, and Department of Muggle Artifacts in recent years.
Many at Hogwarts have begun to suspect Calutain may be behind the strange - and sometimes deadly - problems that have plagued the school this year. Steve the Diavolera first mentioned the Blue Man as the instigator of trouble in Episode 1, and a recent prophecy suggests that Calutain will be responsible for Chester Flutey's death; the later revelation that Flutey was once a very close friend of Calutain added an unusual dimension to that prediction.