Radagon of the Golden Order

Radagon is a champion of the Golden Order, former husband of Queeen Rennala and King Consort of Queen Marika.

Following the Night of Black Knives, Marika shattered the Elden Ring, breaking the Golden Order. Radagon, on the other hand, remained loyal to the Golden Order, and attempted to repair the Elden Ring with the same hammer used to shatter it. As punishment, Marika was imprisoned inside the Erdtree. While Radagon had opposed Marika's treachery, he would share Marika's sentence, as the two were now bound in a single body.

(Source: Elden Ring Wiki)