THE RECLUSE - someone who is isolated and does not communicate with co-workers.
The Recluse is the person who hides in his office and avoids interaction with others. As long as he is doing his work, his isolation may not be an issue. But if his reclusive habits clog the information pipeline in your office, the Recluse becomes a problem for you as a manager trying to keep lines of communication open - and for you as a co-worker who needs to interact with peers to do your job. If the Recluse is your boss, you'll be deprived of critical direction and guidance.