Cerberus is one of the main characters of Clamp's manga and anime series Cardcaptor Sakura. His name is more commonly known in its romanized version, Keroberos, which is also often shortened to Kero-chan or just Kero.
In the Japanese version, he is voiced in his more common "hidden" form by Aya Hisakawa who also voices Yuki Sohma, Retsu Unohana and Masaya Onosaka in his "true" form who also voices Zhao Yun, Zhuge Liang, Issac Dian, and Vash the Stampede.
In the English version, he was voiced in the series by Matt Hill (borrowed form) and Richard Newman (true form), Wendee Lee (borrowed form) and Dave Wittenberg (true form) in the second movie and currently, Mikaela Krantz (borrowed form) and Christopher Sabat (true form) in Cardcaptor Sakura: Clear Card. The former two of which also played Sailor Mercury and Vash the Stampede and the latter of which also played Kurogane, Piccolo and Alex Louis Armstrong.