Horned Lord

The Horned Lord is an unseen character in Game of Thrones, appearing only in the only appears in "The Complete Guide to Westeros: The History of the Night's Watch and the Night's King" featurette. He was a King-Beyond-the-Wall of the Free Folk.

The Horned Lord led an invasion of the North but was defeated by the combined efforts of House Stark and the Night's Watch.

In the books
In the A Song of Ice and Fire novels, the Horned Lord was an ancient King-Beyond-the-Wall who raided south of the Wall. A quote is attributed to him: "Sorcery is a sword without a hilt. There is no safe way to grasp it."