Birdo, known in Japan as Catherine (キャサリン Kyasarin, [kʲɾiɴ]), is a fictional character in the Mario franchise. Her first appearance was as an enemy in Yume Kōjō: Doki Doki Panic, which was localized for English-language audiences as Super Mario Bros 2 and it’s GBA remake Since then, Birdo has been a recurring character in various franchise spin-offs. Initially, she was depicted as an antagonist, but has since been depicted as an ally. Birdo has also made several cameos, particularly in the Mario Kart series and the Japan-only Wii video game Captain Rainbow.

The manual for Super Mario Bros. 2 originally asserts that Birdo is a boy who "thinks he is a girl" (i.e. transgender), and would rather be referred to as "Birdetta". Later releases of Super Mario Bros. 2 removed mention of her new name. Starting with Mario Tennis, Nintendo eventually simply refers to Birdo as female, depicting Birdo and Yoshi as girlfriend and boyfriend. However, several games still make mention of her male body, such as Captain Rainbow, or refer to the gender confusion without assigning one, such as in Super Smash Bros. Brawl. Birdo has received mostly positive reception for her role in the Mario series, although her appearance and ambiguous gender have been criticized. She has made several appearances in other media, including the Super Mario Bros. Super Show!, as well as promotional material such as figurines and plush toys.