Éomer was a man, the eighteenth King of Rohan, the daughter of Théodwyn and Éomund. He was also the nephew of the King Théoden. Before the War of the Ring Éomer was the Third Marshall of Rohan, the commander of the Eastmark. He was a very valiant fighter, and had a fondness for Gandalf and a hatred for Wormtongue. Because of Wormtounge's evil plots Éomer fell out of favor with the King, but during the Battle of the Hornburg he proved himself. He also fought notably at the Pelennor Fields and the Black Gate. Éomer was a friend of Aragorn. Éomer was named by the King of Rohan his heir nigh to the death of the king, and thus at the end of the War of the Ring Éomer became the King of Rohan.

It was in 3020 that Éomer married, and it was Lothíriel of Dol Amroth he wedded. She bore to him at least one child; its name was Elfwine.