Prosper is an Orlesian noble featured in Mark of the Assassin.
Background
Presently, nothing is known of Prosper's background.
Involvement
Prosper is apparently an antagonist in the Mark of the Assassin DLC. According to Tallis, he holds the "Heart of the Many", supposedly a gem which he has no right to possess. Tallis enlists Hawke's aid to infiltrate Prosper's home, the Château Haine, and steal the Heart of the Many.
Hawke and company arrive at the Château, having apparently accepted Prosper's previous invitation to the Champion of Kirkwall. After slaying a wyvern during a hunt, Prosper welcomes the Champion into his home. But as Hawke and Tallis infiltrate his vault, it is revealed that Prosper knew who the latter was the whole time and had the two imprisoned. As Tallis explains to Hawke, there never was a jewel. She was in fact after a Tal-Vashoth named Salit, who was going to sell confidential information about the Qunari to Prosper. But instead of plans for weapons or tactical information, Salit gave Prosper a list of names, detailing the various Qunari agents in Thedas, which Prosper failed to see the significance of. In the ensuing battle, after the Champion escaped from his dungeon, Prosper was nearly sent off the side of a cliff with his wyvern mount Leopold. He promised that Empress Celene would burn Kirkwall to the ground, before making one last attack at Hawke and then fell to his death. However, his threats were futile, as if it became public knowledge that he was dealing with Tal-Vashoth, it would cause a scandal.