Bael

When Beelzebub is away, Bael acts as the king for him. To substitute for his friend, who is always in danger of being assassinated by angels, he changes his appearance to resemble Beelzebub and faces angels that invade Avisos.

Bael is Beelzebub's best friend and even has the same sexual orientation. He is also the devil Beelzebub contacts most often, But Bael doesn't think so. (Bael: You call texting 4 times a year 'often'?!)