The Archmage: As a Keeper, he is an incredibly powerful mage.
Bald of Evil: He looks like an elven Lex Luthor.
Blood Magic: He created Witherfang and the werewolf curse using his own blood as a catalyst for the ritual (granting him immortality as long as the curse is active as a bonus).
Dying as Yourself: Ilona convinces him to let go of his rage and end the curse.
Fantastic Racism: He hates humans. More specifically, he hates the human tribe that used to live in the forest. He's polite enough to Ilona.
Heel Realization: Zathrian comes to realize that his anger has turned him into a monster.
Zathrian: “Perhaps I have lived too long. This hatred in me is like an ancient, gnarled root...it has consumed my soul.”
Immortality Immorality: He can't die of natural causes as long as the werewolf curse exists.
His apprentice, Lanaya, relates a story of how he slaughtered a group of bandits who murdered one of his clan's scouts.
This is also the reason why he unleashes the curse on humans - they destroyed his children. His son was beaten to death and his daughter was raped and committed suicide when she learned that she was pregnant.
Parental Substitute: Serves as one to Lanaya after rescuing her. She relates that he offered to take her back to her family, but she had no notion if she had any other living relatives, and wanted to stay with the man who had rescued her.
Redemption Equals Death: He lets go of his anger and releases the curse.
Replacement Goldfish: There's an implication that he sees Lanaya as this for his deceased daughter, since he found her being forced to serve as a "servant" for a group of bandits with the heavy implication that they sexually abused her.
Revenge Before Reason: He refuses to lift the werewolf curse even after it's pointed out to him that all he's doing anymore is punishing the descendants of the men who killed his family.
Zathrian: “I will not lift a finger to help the descendants of savages who deserved the curse they received.”
Roaring Rampage of Revenge: Why he unleashed the curse and lets it continue.
When a group of bandits killed a clan scout who strayed too close to their camp, Zathrian personally tracked the bandits by himself for a month, then attacked the group and killed every last one of them single-handedly.
The Stoic: Not openly emotional unless the topic shifts to his family, then he becomes Not So Stoic.
Treacherous Questgiver: It's clear he wasn't being forward about the entire situation once you meet The Lady of the Forest.
Who Wants to Live Forever?: Ilona convinces him that his long life has only succeeded in making him more angry.