The following information is from the Adventure Time comic book series. It may not be part of the same canon or continuity as the animated series.

Randall N. Byron (or Kewlboy) is the creator of the computer program Ewlbo. He had a great interest in computer and video games. He created a code that infects games and allows his characters to become stronger and on occasion give them his face.

1,002 years ago, the first Mushroom War occurred and he programmed a software version of himself in order to survive. Meanwhile his code merged with a military program called the Omega Algorithm and became the computer virus Ewlbo and began systematically infecting and destroying computer systems and replacing them with its own personality. Randall attempted to merge with Ewlbo in order to control it but ended up getting overwritten by the virus. However, Ewlbo was a slob virus and never emptied his trash basket and Randall was able to undelete himself after Ewlbo's defeat. He now resides inside of BMO's Main-Brain-Game-Frame.