Diagna is a Yokudan, who had a cult of Redguards later devoted to him. He originated in Yokuda during the Twenty Seven Snake Folk Slaughter. Diagna was an avatar of the HoonDing, another Redguard deity, that achieved permanence. He was instrumental in the defeat of the Lefthanded Elves, as he brought orichalc weapons to the Yokudans to win the fight.
In Tamriel, he had a number of followers, who called themselves the Order of Diagna. This order was responsible for defeating the Orcs during the Siege of Orsinium, and then fading into obscurity, with him now being little more than a local power spirit of the Dragontail Mountains.