Legion: The Many Lives of Stephen Leeds

Stephen Leeds is perfectly sane. It's his hallucinations who are mad. 

  A genius of unrivaled aptitude, Stephen can learn any new skill, vocation, or art in a matter of hours. However, to contain all of this, his mind creates hallucinatory people--Stephen calls them aspects--to hold and manifest the information. Wherever he goes, he is joined by a team of imaginary experts to give advice, interpretation, and explanation. He uses them to solve problems...for a price. 

  His brain is getting a little crowded and the aspects have a tendency of taking on lives of their own. When a company hires him to recover stolen property--a camera that can allegedly take pictures of the past--Stephen finds himself in an adventure crossing oceans and fighting terrorists. What he discovers may upend the foundation of three major world religions--and, perhaps give him a vital clue into the true nature of his aspects.