Luther Hargreeves a.k.a #00.01 and Spaceboy is the leader of the team and twin brother to #00.05, The Boy. He is codenamed Spaceboy due to his accomplishment of being the youngest person ever to become an an astronaut. It is unsure as to whether Luther's codename was chosen by himself, Hargreeves or the media, as a poster of 'Spaceboy - The first boy in space' is shown in The Umbrella Academy: Apocalypse Suite.
Spaceboy was involved in a disastrous mission to Mars. His head was attached to the body of a Martian Ape and has gained all the physical abilities of one, after Hargreeves performed a life saving surgery on him.
In Apocalypse Suite it becomes clear Spaceboy has romantic feelings for The Rumor. They kiss once, but after this Spaceboy thinks he is too monstrous for her to ever love him back and have a decent relationship.