Cullen is a Templar that was originally stationed at the tower in Ferelden. He was mistrustful of mages, but he also developed feelings for a mage in the Ferelden tower. However, being a man loyal to the oaths and vows he had taken Cullen would never pursue such a relationship. When the tower was infested with demons due to blood mages he was imprisoned by them and then mentally and physically tortured. After his torture he came to outright despise all mages and want them either slaughtered or put under strict watch and limitations.
After the blight he moved to the Kirkwall circle. During the Templar, mage disaster there he came to question the system and disagreed with the knight-commanders annulment order, encouraging her to reconsider. Afterwards he left the Templar order and accepted an offer to become the commander of the Inquisition's forces. Cullen attempted to get off the addictive lyrium that Templar's are forced to take. He also came to have an unbiased, more positive view and feelings toward mages.