False Bowser is a counterpart of Bowser in the form of a False Character. He only appears in Adventure Mode: The Subspace Emissary in Super Smash Bros. Brawl, and like other False Characters, False Bowser was created from Shadow Bugs.
The False Bowser makes its first appearances in The Lake, where it attacks Fox and Diddy Kong at the very end of the stage. Once they defeat False Bowser, his trophy dissolves, and then the real Bowser makes his entrance and tries to capture both Fox and Diddy.
Another False Bowser reappears in the opening cutscene for The Lake Shore after Bowser uses a Dark Cannon on the princess who was rescued from the Midair Stadium, who is either or Princess Zelda or Princess Peach. False Bowser is ordered to dissolve into Shadow Bugs to swarm on and duplicate the trophy of Peach or Zelda.