User blog comment:Madman97/The Aedra Vs. The Daedra theory/@comment-3025184-20131010203442/@comment-25109952-20131011204627

StarkBlack is correct. Alduin is a Mirror Image of Alatosh, the Nordic version of him. Once a God is worshipped enough, or somebody dances on the Towers, the God literally comes into existance. Tsun actually proves this in-game, by simply being a character. Tsun is the Nordic version of Julianos. When people worship Julianos, they get his blessing. Of Julianos. But Tsun is dead, and cannot give blessings. He can only interract with those within Sovngarde, therefore he is a Mirror Image of Julianos, as they both cannot be present in Sovngarde and giving blessings at the same time.

Source : SajuukKhar.