Board Thread:Lore Discussion/@comment-184.98.87.191-20161228010804/@comment-173.81.113.240-20170127222412

The Protagonist is practically proclaimed the Last Dragonborn due to the prophecy of Aludin's Wall, that when the World-eater returns, the wheel will turn to the Last Dragonborn. The Skyrim game did feature Aludin's appearance but this was merely from him being sent forward in time, its possible that the protagonist in Skyrim is not the Last Dragonborn. This is because they mention that Aludin is defeated but not dead, his soul was unable to be absorbed making his return and and the importance of another Dragonborn paramount.

Also Dragonborn are very rare in the world, only appearing in times of great need or when things need to change. Tiber Septim was born a Dragonborn and created the Third Empire, its possible that at some point, when Aludin returns for real, a new dragonborn could return to kill him.