The Hobgoblin Thief is a unique Hobgoblin in Balduir's Gate. There are technically two in-game, one found near the Beregost Cave in the Area South of Beregost, the other found in the middle of Ulcaster's map. They are immediately distinguishable from other Hobgoblins by their incredibly dark skin and bright green tunic.
They are noteworthy for having a pair of Boots of Stealth, related to a quest received in Beregost. Oddly enough, you may find a single pair on each of them, despite only one pair being stolen. In BGEE, this is fixed, as when one is dispatched, the other Hobgoblin still spawns but without the boots.