Fake Bowser is a fake version of Bowser. When Fake Bowser was born, only Bowser knew who his parents were. 500 years later, after Fake Bowser gave up looking for his parents, he decided to live with Bowser. He is also has a crown on his head instead of hair.
History
Early Life
Fake Bowser was created by the creators of Super Mario Super Show to be a replacement for the real Bowser, who just burned Mario and Luigi to death in the pilot (which is how Mario and Luigi died.) Plus, the creators couldn't afford the real Mario characters (except the Toads, but only one), so they created a Fake Bowser and paid for the less-expensive New Mario Bros, who put on the clothes of the Mario Bros before them and pretended to be them for the show's 65-episode run.
Later Parts Of Fake Bowser's Life
He danced every day and every night. Sometimes Laa-Laa would join him, but it was really just an assassination attempt. Fake Bowser once danced so hard, that he almost killed Mario, but he escaped.
Jobs Today
He is also the feared marshall of The Bubble Bass Empire. We suspect this is due to a combination of bribes and rabid puppies. He was also once a friend of Fluttershy, until she was cured and forgiven by Chuck Norris.