Bowser Junior

Bowser Koopa Junior is a fictional character from The Mario Universe. He appears as the Youngest of King Bowser's children. Unlike his siblings he first appeared in Mario Party 3. His biggest appearance was in Super Mario Sunshine where he used his alter ego known as Shadow Mario to frame Mario for polluting Isle Delfino. After that Bowser Junior appears in Mario Party 4, Mario Party 5 and Mario Kart Double Dash.

Sadly enough Bowser Junior won't be joining his siblings when they return in Mario and Luigi's Superstar Saga.