In any other origin, you meet him in the Tower of Magi quest (Broken Circle) - he is the Templar in the pink bubble, held there against his will by a desire demon, right before you go up to the harrowing chamber to confront Uldred. At the beginning of the Mage origin, Cullen is the Templar who is chosen to kill your character should he/she fail their harrowing and become an abomination. Cullen is a Templar whom you first meet in Dragon Age: Origins.
