He resides in Limbo, helping some spirits move on to a higher place and generally keeping an eye on Marty. He's the one that's taught Marty how to use his powers and develop new ones.

The face he shows to Marty isn't his real one but merely an image that was best to provide a feeling of comfort and friendliness when Marty first arrived. Likewise with his 'house'. The room's walls drift slowly around creating an illusion of a substance but they aren't really there.

Nothing is known of his background, but his clothes indicate that he has been around for many years as part of his white wardrobe appears to be from Regency times.

He often tries to guide Marty using poetry that doesn't always quite rhyme and which does more to confuse than aid the poor ghost.

Generally quite happy to let Marty learn his own lessons in death, he will, on the odd occasion, intervene where necessary and if he has the power to do so.