King of Narnia, in The Last Battle, Book 7 of The Chronicles of Narnia by C.S. Lewis. He and his friend Jewel the Unicorn discovered that a charlatan Ape named Shift was tricking Narnians into slavery for the Calormenes through a false Aslan, Lord of the Narnians. He was imprisoned for protesting when Shift alleged that Aslan and Tash, the blood-god of Calormen, were the same entity.
Eustace Scrubb and Jill Pole, visitors from our world, rescued him. From there Tirian's plans rapidly disintegrated. Their efforts to unmask the deception were met by Narnian apathy; the Dwarves they encountered ceased to believe in Aslan, or kings, or anything else but self-interest. They abandoned the effort and attempted to rendezvous with his allies at the Narnian capital Cair Paravel; they soon discovered that Cair Paravel had fallen to the Calormenes.
With no hope of aid, Tirian, Jill and Eustace returned to the Stable Hill where Shift was performing his deception. They rallied as many Narnians as they could to the last battle, but they were outnumbered and forced into the stable. The stable door was in actuality a gateway to the True Narnia, Paradise itself. From there Tirian witnessed the end of old Narnia, met the true Aslan and earned his eternal reward as the Last of the Kings of Narnia.