He is a lanky, dark-skinned old man who is an expert on history. He tends to ramble on about things and has been coined a walking Wikipedia. He has been mentioned as quite old, and Stephen seems finds his voice quite comforting.
His insanity is that he hallucinates about an astronaut named Stan in space who lives on a satellite, who occasionally sends him weather information. Stan is not one of Stephen's hallucinations, but is Tobias', and neither he nor any of the other aspects have ever seen him or heard of him. Stephen also mentions that Tobias has schizophrenia, although it is not mentioned if he has shown any of the symptoms of it other than seeing Stan.