Dulin Forender is the trusted second of Lord Pyral Harrowmont. He is seeking to protect his lord from Bhelen's machinations, so the Warden must prove themselves before he will allow them to see Harrowmont.
If the Warden is a Dwarven Noble, even if the origin story ended with the Warden convincing Harrowmont that Bhelen and possibly Trian framed them, Dulin will state that the Warden and Bhelen previously allied to remove a rival, presumably Trian.
After you talk to him, accept the quest and head to the Proving arena, Dulin will be waiting at Tapster's Tavern in the Orzammar Commons. Upon completion of the Proving, Dulin will escort the Warden to Harrowmont.If Harrowmont is made king and the Warden makes the Ultimate Sacrifice, Dulin is seen at the latter's funeral.