quote Wikipedia

Baby Bowser (or Bowser Junior) is one of 2 things in the Mario series: 1. Bowser's younger incarnation or 2. Bowser's son. The first one caused trouble for Yoshi in Super Mario World 2: Yoshi's Island. He also took the Super Happy Tree in Yoshi's Story. The second one was a mischevious, trouble-making Koopa Kid who fouled up Isle Delfino in Super Mario Sunshine disguised as Mario so the famous plumber would be blamed for it. Junior kidnapped Peach because Bowser told him she was Junior's mama. He took her to Corona Mountain where Bowser was. Mario later defeated father and son. Bowser confessed that Peach wasn't Junior's mother. Junior then wanted revenge on Mario. Junior also appeared in Mario Kart: Double Dash!!, Mario Golf: Toadstool Tour, and Mario Power Tennis as a playable character. Baby Bowser/ Bowser Jr. also has a significant role in the Mario Party games. In the original, he acted as Toad on the Eternal Star board, challenging players to dice roll matches to determine whether they deserved a star. In Mario Party 2, he was a character on the boards, taking five coins from passersby and changing into Bowser should anyone ever obtain a Bowser Bomb. His role in the next two games of the series is minor, except for cameo appearances in certain mini- games and running the buildings on the boards, but in Mario Party 5 he became a playable character as well as a villain in Story Mode (though he bore the name Koopa Kid, which debuted in Mario Party 4).

quote Wikipedia

Baby Bowser (or Bowser Junior) is one of 2 things in the Mario series: 1. Bowser's younger incarnation or 2. Bowser's son. The first one caused trouble for Yoshi in Super Mario World 2: Yoshi's Island. He also took the Super Happy Tree in Yoshi's Story. The second one was a mischevious, trouble-making Koopa Kid who fouled up Isle Delfino in Super Mario Sunshine disguised as Mario so the famous plumber would be blamed for it. Junior kidnapped Peach because Bowser told him she was Junior's mama. He took her to Corona Mountain where Bowser was. Mario later defeated father and son. Bowser confessed that Peach wasn't Junior's mother. Junior then wanted revenge on Mario. Junior also appeared in Mario Kart: Double Dash!!, Mario Golf: Toadstool Tour, and Mario Power Tennis as a playable character. Baby Bowser/ Bowser Jr. also has a significant role in the Mario Party games. In the original, he acted as Toad on the Eternal Star board, challenging players to dice roll matches to determine whether they deserved a star. In Mario Party 2, he was a character on the boards, taking five coins from passersby and changing into Bowser should anyone ever obtain a Bowser Bomb. His role in the next two games of the series is minor, except for cameo appearances in certain mini- games and running the buildings on the boards, but in Mario Party 5 he became a playable character as well as a villain in Story Mode (though he bore the name Koopa Kid, which debuted in Mario Party 4).