Kerberos

Kerberos is Virgyl's dog. He's a puppy of a pug. He is probably inspired by the mythological monster Cerberus, the three-headed hound who stands guard at the gates of the Underworld.

While Virgyl seems perpetually annoyed with him, in episode 1.8 he asks Baal to take care of his dog in the event of Virgyl's death. He asks Baal to take Kerberos on 'lots of adventures'.