Despite his own arcane abilities, Ethan preferred to keep out of the impending mage/templar conflict, remaining neutral when possible. The only exception being his attitude towards blood magic, which he avoided using for all but emergencies.
Flipped a coin to decide his "allegiance". It came up tails so he defended the mages.
Rival-Romanced Anders, though trusted him enough to distract the grand Cleric.
Befriended Carver, who joined the expedition and became a Grey Warden.
Befriended Varric and healed Bartrand, but did not allow him to keep the lyrium shard.
Obeyed the law when possible, much to the delight of his friend Aveline.
Befriended Fenris, killed Danarius, but spared Varania.
Had casual sex with his friend, Isabela. Killed Castillon.
Lost Merrill as a friend and developed a bitter rivalry with her by refusing to allow her to use blood magic to achieve her goals.
Maintained friendly relationship with Sebastian, though abandoned by him after reluctantly sparing Anders.
Earned the Arishok's respect and duelled him, emerging victorious.
Sent Feynriel to Tevinter.
Owed Anders a life-debt due to his saving Carver in the Deep Roads. Did not kill him, but sent him away for good.
Hired a cleaner to remove the 10 year-old corpses in Fenris' home.