Legion

Stephen Leeds has a mental condition that causes him to hallucinate many different people. These "aspects" have their own personality strengths and weaknesses. He knows they are not "real", yet he treats them as real. They must "travel" to meet him. He opens doors for them. He books space on airplanes for them. They must use a phone if they want to talk remotely. His aspects give him near super-human power. He can simply glance at a foreign language book and one of his aspects can know help him speak a foreign language. He uses this skill as part of a unique private investigator-like business that has made him a rich man. He also has many people eager to study him.
The audiobook contains three novellas: Legion, Legion, Skin Deep, Legion: Lies of the Beholder. The first few books are regular adventure story, while the last one starts to tear apart his special abilities. The books are an interesting exploration of possible benefits of extreme mental "differences". Rather than treat them as illnesses, treat them as different benefits.