The Avatar of Akatosh was the form Martin Septim took when he shattered the Amulet of Kings upon the altar at the Temple of the One, combining the blood of Akatosh with his own. This transformed him into a brilliant Golden Dragon and he used this form to banish Mehrunes Dagon back into Oblivion and save Tamriel.
After the battle this form was frozen in stone for all of the Imperial City to see. Thus ending the Septim Dynasty, and preventing the need for an Emperor to protect Tamriel from invasions from Oblivion.
- There may be confusion as to whether the dragon is Akatosh himself, or merely his Avatar. This is easily resolved: on PC, using console commands to select the statue, it is listed at "AvatarofAkatosh".