Cornelius

Doctor Cornelius was the important mentor, advisor and teacher of the young King Caspian X. As a person of half-dwarfish, half-human blood posing as a human, he was one of the few people in the Telmarine-ruled society of Narnia under King Miraz that knew of the history of the Old Narnians, and introduced Caspian to them.

In Prince Caspian
When Doctor Cornelius is first introduced, he is to be the tutor of Prince Caspian X and to teach him the basics of art, science, history, mathematics and music. He eventually learns of Caspian's former nurse, who was like Cornelius, a half-dwarf, and learned that Caspian was interested and favorable of the past of Narnia, which he had been taught to be fairy-tales from his tyrannical uncle and adoptive father, King Miraz. Doctor Cornelius tells Caspian of Narnia's true past and that Miraz was a usurper who killed his father. When a son is born to Miraz, he helps Caspian escape the castle, saving his life, since he knows Miraz will want his own son to be King. Doctor Cornelius rejoins Caspian after he joins the Old Narnians, helping him organize an army and advising him in tactics. Cornelius is responsible for finding and giving Caspian Queen Susan's Horn, which transported the Pevensies back to Narnia, and sending Trumpkin to the coastal location of Cair Paravel to meet them. After Caspian ascends the throne, he makes Cornelius his Lord Chancellor.