Little is known about the man who infiltrated al Qaeda in Yemen and ultimately foiled an underwear bomb plot targeting a U.S.-bound plane. But a few details have emerged about the agent in recent days. He is of Arab descent, has lived in the United Kingdom for many years, and holds a British passport. He was originally recruited by Saudi counterterrorism agencies because he had fallen in with a group of jihadists, which gave him the background to fit in with the terror network.