Feldan is a pyromancer – a wizard specializing in fire magic. He was one of the original party members who set forth on Boroman ’s quest.
There was some friction with him and the rest of the group due to a disregard for the welfare of his friends, and their location when he was laying a massive fire spell down. This led to near violence with Min after he burned her horse, Artax.
Feldan went missing in Sharn after going invisible to follow Leonard, the official that had denied their papers for travel.
Ralenir approached the party while in a warehouse in Sharn, where the party was in the midst of an investigation. This fire-mage had come with papers from Boroman, and intended to take the place of Feldan, who had gone missing.
Ralenir eventually revealed himself to be Feldan in disguise, and worse yet appears to work for Rien Acar, his old professor at Morgraive University. He appears to have at least partially orchestrated the set-up that led to the arrest of the party in Stormreach.