As Lancelot, during his adventures in Gore, led a rescue party to the Water Bridge in search of Gawaine, they were met by a dwarf riding a great hunting horse and carrying a whip to control it. The dwarf asked for Lancelot, promising to lead him to an excellent place, for his own profit, and bring him back shortly – provided he came alone. Lancelot trustingly did so and ended up being held prisoner in an isolated tower, guarded by Meliagrant’s seneschal and his wife.
Those who had been with Lancelot later described the dwarf as stunted, hunchbacked, and grimacing; their memories of his appearance might, of course, have been colored by realization of his treachery. In any event, he would presumably have been either one of Meliagrant’s servants or else acting for pay.