Varen Aquilarios is the son of a Colovian duke and leader of a rebellion against Emperor Leovic. Finally, Varen took the crown himself. He's member of the Five Companions, who sought the artifact The Amulet of Kings. With this amulet, the group wanted to persuade Akatosh, the dragon god of time, to accept Varen as Dragonborn.
Obviously only a true Dragonborn can ignite the Eternal Dragonfires in the Imperial City.