Alduin - History

Prophecy
The prophecy of Alduin is foretold on Alduin's Wall, located at Sky Haven Temple. The wall prophesies chaos after the murder of the High King of Skyrim as well as the destruction of Tamriel. It is also said that only a Dovahkiin (Dragonborn) can defeat the enraged god Alduin by harnessing the power of the dragon in the form of dragon shouts to ultimately destroy him in one final battle to restore peace.

Beginning
Alduin was the first dragon among many that ruled over men. The dragons viewed humanity as a lesser species, and kept a tyrannical hold on mankind, but soon, in an event known as The Dragon War, men stood up to their dragon overlords, and learned how to use the Voice (Dragon Language). On the Throat of the World, Alduin was defeated, but not killed. Instead, with an Elder Scroll, Alduin was sent in time unintentionally, and would not return until 201st year of the Fourth Era, which is when Skyrim takes place.

Climax
After Delphine, the last of the Blades who discovered the Dragonborn of the Fourth Era, she helped discover from Paarthurnax that the key to Alduin's defeat was the Dragonrend shout. Septimus Signus, an expert on Elder Scrolls, helped the Dragonborn locate an Elder Scroll in Alftand, which the Dragonborn used atop the Throat of the World to view the memory of Alduin's initial defeat. Attracted by the power of the scroll, Alduin appeared. Together with Paarthurnax, the Dragonborn weakened Alduin, who in turn fled the battle.

"Demise"
The Dragonborn finally kills Alduin in Sovngarde alongside the three other heroes of Sovngarde, Hakon One-Eye, Felldir the Old, and Gormlaith Golden-Hilt. Alduin is banished from the world but Arngeir and Paarthurnax theorize he may return in the future to fufill his destiny as the World-Eater.