Formerly known as Antikrist, they changed their name in December 1995. All in all they were only known as "Antikrist" for about a month.
In Norse mythology, Månagarmr is another name for the wolf Hati, referring to his hunting down the moon during the Ragnarök and swallowing it. The name can be anglicized as Managarm, Månagarm or Managarmr.