Specialist

A specialist has incredible depth on a single subject, and can almost always get "his" or "her" questions on that subject. These subjects range from niche subjects like "psychology" to wide swathes of the canon like "literature" and "history". Specialists typically have some knowledge outside their area or areas, but not enough to be considered a true generalist. Many specialists later fill in knowledge gaps in all subjects to become full-fledged generalists.