Hakon One-Eye

 was a Nord hero who overthrew the dragons in ancient times. He can be seen in The Throat of the World and in Sovngarde.

History
Hakon, along with Felldir the Old and Gormlaith Golden-Hilt, fought Alduin atop The Throat of the World during the Dragon War.

After Gormlaith Golden-Hilt was killed by Alduin, Felldir the Old used the Elder Scroll to banish Alduin before he could stop them. The use of the Elder Scroll created a time wound that remains to the the present day.

Interactions
During Sovngarde, he helps the Dragonborn defeat Alduin in the main questline. Upon completion of Sovngarde, Hakon One-Eye can be summoned to fight for you with the Call of Valor shout.

Trivia

 * Hakon's voice actors are different in Time wound and in Sovngarde.