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.
Some of the more successful teams to make the specialist model work include the 2008-2011 Harvard squads, which featured a strong science player (Andy Watkins), a strong literature/fine arts player (Ted Gioia), and a strong history player (Bruce Arthur, with Dallas Simons also good in this category as well as myth). While all of these players are fine generalists to varying extents, it was generally considered one of the finest specialist-based squads in recent years.