Baby Bowser

Baby Bowser is a recurring villain in the Yoshi series designed to be the baby form of Bowser. Although not related to him, Kamek was mainly responsible for his child rearing.

Super Mario World 2: Yoshi's Island
Baby Bowser is the final boss battle in Super Mario World 2: Yoshi's Island. However, he didn't seem to be too involved with Kamek's plans at capturing the Baby Mario brothers. He appears in Bowser's Castle when Kamek demands that Yoshi hand over Baby Mario at the end of the level. The area turns to his room, after which Baby Bowser complains about Kamek making noise that woke him up and literally pounds him flat as paper kicks him away. He then notices Yoshi and immediately wants to ride him. He would try to kick Baby Mario off Yoshi's back and ride Yoshi himself. He would also send out shock-waves by ground pounding.

Yoshi's Island DS
During the events of Yoshi's Island DS, Baby Bowser was at his castle when Bowser shows up from the future to kidnap the Star Children and gain control of the universe. His younger self was (ironically) abducted by the Kamek from the future and brought to Bowser's castle. When Baby Bowser realizes what's going on, he insults his grown-up self and his plan, calling him an "old geezer". Enraged and oblivious to the fact that his younger self was one of the Star Children, the Koopa King kicks Baby Bowser out of the castle. He then becomes playable after being found, first playable in World 4-5.