Guest is a dark-haired android-robot-humanoid-thing built to essentially serve as company for those who are lonely. To be a Guest, if you will. He was made in 2013 canonically, and is actually based off of MePad (Inanimate Insanity) and BMO (Adventure Time).

In his Epithet Erased storyline, he is... "friends" with Giovanni Potage.

His other storylines are very tangled, so I personally like to take his EE storyline as the "canon" one.