Legion novels (Brandon Sanderson)

"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...