Beelzebub IV (ベルゼバブ4世, Beruzebabu Yonsei), full name Kaiser de Emperana Beelzebub IV (カイゼル・デ・エンペラーナ・ベルゼバブ4世, Kaizaru de Emperāna Beruzebabu Yonsei), and abbreviated to Berubō (ベル坊, Berubō), is the Demon King. Beelzebub is the son of the Great Demon King.
Beelzebub is a baby with an abnormally wide build and green hair. Sometimes, he wears a yellow pacifier. Usually, he is seen nude to his genitals, even to the public, causing ordinary people to chatter about him and his "parent" Tatsumi.