Bowser Jr is a member of Bowser's army and the Koopa King's only child. He is usually a secondary antagonist, but he has been the main one on occasion.
Bowser Jr looks like a miniature Bowser with beady eyes, but he only has two normal metal wristbands on his arms. He usually wears a bandanna with fangs on it, though in Super Mario Sunshine he wears one with Mario's mustache on it.
- Bowser Jr is the only truly legit kid of Bowser; the Koopalings have recently been clarified as not being such themselves.
- New Super Mario Bros. and Super Mario Sunshine are the only games where Bowser Jr is the primary antagonist. In the latter he is usually as Shadow Mario.