The Collector was a human murderer in Betrayal at Krondor. He can be encountered in Chapter 1.
The Collector killed Stellan of Eggley, who owed him a debt, uncaring that Stellan had been a key figure in Eggley's annual festival that year. Proceeding to Tanneurs, where a gambler at the Inn also owed him money, he took up residence in the Inn's back rooms. Word of his presence and Stellan's murder spread throughout the Inn, and the gambler ceased to ply his trade for fear the Collector would see the money owed him being gambled away.
Having learned of the murder from Devon in Eggley, the party discusses the Collector with the high priestess of Temple of Silban, who offers them a reward if they send the Collector to her. If they speak to the Collector in the Inn's back room at Tanneurs, they can tell him someone at the Temple of Siliban owes him a debt, prompting him to leave for the Temple the following morning. Returning there, they can learn that the Collector is now in the Temple's custody, to be rehabilitated if he lives after his punishment. The party receives a small sum of gold and some healing potions as a reward.