The Murder Magician was a villain that the Umbrella Academy faced in an early adventure. He appeared in the short story "...But the Past Ain't Through With You" and is a major character in the third series "Hotel Oblivion."
The Murder Magician and his sidekick "The Assistant" were criminals with the intent of becoming famous by going on homicidal rampages. Their first known victim was the duplicate The Rumor, who they encountered in an alley (after being tipped off by The Monocle) and sawed in half.
For this he won the Oppenheimer Prize for Villainy at the Annual Summit of Dastardly Deeds, along with a substantial cash prize that went along with it. Using the money he received, he went on The Lucifer Clark Show to brag of his accomplishments, and unveil his latest carnage causing creation, "The Murderbot." He unleashes the Murderbot on the studio while he and The Assistant attempt to add the show's host Mr. Clark to their list of victims. They were stopped by the arrival of the Umbrella Academy where The Murder Magician was rendered unconscious by a punch from The Kraken. He was presumably apprehended.
"Hotel Oblivion" opens immediately after being apprehended, with Hargreeves sending placing the Murder Magician in the Hotel, an interdimensional prison for supervillains.