Larius was the Warden-Commander who had left the order to go to his Calling after thirty years living as a Grey Warden. The influence of the imprisoned Corypheus drove him insane. He claims to have died once, but still be alive. He is extremely lucid for a man who is on the verge of becoming a ghoul, on top of being influenced by Corypheus, being able to tell Hawke much of the history of the prison tower and their father, Malcolm.
Larius was the Warden-Commander responsible for re-sealing the prison built by the Wardens to contain Corypheus. Fearing the ability of Corypheus to influence any entity with the Darkspawn Taint including Grey Wardens, the Wardens sought a non-Warden Mage to re-enforce the seals. Larius chose Malcolm Hawke for the task. Malcolm Hawke was initially reluctant and a desperate Larius delivered an ultimatum; aid the Wardens or never see Leandra Amell again. Malcolm agreed in exchange for the Wardens arranging to protect Leandra in his absence and that her father be "convinced" to allow Leandra to leave Kirkwall with Malcolm and not pursue her. With their mission complete, Larius returned to his duties and served as a Grey Warden until the time came for his calling.
In the Legacy DLC, Hawke will encounter the still living Larius wandering around Corypheus prison. Through his partially coherent ramblings, Larius will reveal the nature of Corypheus, the prison and the nature of the seals.
Eventually Hawke must choose between Larius and Janeka regarding what to do with Corypheus. Larius argues for killing him as the seals keeping him imprisoned are deteriorating, whereas Janeka wishes to free him, confident that she can use blood magic to control him and use him as a weapon to end the Blights.
If Hawke sided with Larius first, then Janeka will block their path and send the Carta after them as she races to the top of the keep. If Hawke sided with Janeka first, then Larius will persuade the other wardens to follow him instead.
If Janeka is once again sided with at the Final Seal, Larius will attempt to stop her, but she uses her magic to tear him apart. If Hawke decides to side with Larius after previously supporting Janeka, she will try to kill Hawke, but Larius will tackle her and beat her to death with his bare hands. Larius will then dispatch the remaining Grey Wardens to warn the rest of the order of what has transpired.
If Hawke supports Larius on both occasions, a fight will ensue in which Hawke will be forced to kill Janeka and the other Grey Wardens.
Larius will then tell Hawke that they must break the seals with their blood, and kill Corypheus before he awakens. A battle ensues in which Hawke kills the ancient evil.If he survived when Hawke speaks to Larius after the battle with Corypheus, the former Warden-Commander explains that he has more clarity now that the darkspawn is dead and he can no longer hear him. He repeatedly thanks Hawke for his freedom. As he is walking away from the Champion, he smiles sinisterly. It is likely that Corypheus was able to possess him after his body was destroyed.