Philemon is an important recurring character in the Shin Megami Tensei: Persona series. He is often depicted as a young man wearing a butterfly mask, but appears in later games only in the guise of a butterfly.
The depiction of Philemon as a spirit guide comes from the writings of Carl Jung's Red Book, or Liber Novus.
Philemon is a being who appears as a man wearing a butterfly mask. Living within the realm of the collective subconcious human mind, he is able to awaken within people the ability to summon Personae, as well as granting the Wild Card, an ability to use many different Personae, to extremely powerful humans. Philemon can usually act as a neutral observer as he is unable to directly interfere with human affairs, but he owns a dimension known as the Velvet Room, only accessible to those he has chosen and filled with his servants, who help them hone their Persona powers. Philemon is wagering a bet with Nyarlathotep to see if humanity will eventually become enlightened, or will succumb to their vices and ruin themselves.
While Nyarlathotep is a personification of human malevolence and desire for destruction, Philemon is a personification of human benevolence and hope. The bet between them is meant to see which aspects of the human psyche will eventually triumph over the other. Following Nyarlathotep's defeat during the events of Persona 2: Eternal Punishment, Philemon remains as a guide for people, though their wager has yet to be settled.