He was one of the most skilled magicians in all of Alagaësia but he wasn't among the twelve sent to protect Eragon because he was of noble birth. Däthedr was very good friends with Arya, as well as was present at Ceunon, Gil'ead, and the Battle of Ilirea where Evandar was slain.
Siege of Urû'baen Edit
He was present in the siege, assisting his Queen in battle. After Islanzadí was slain he was assumed to have taken temporary command of the Elven forces. Däthedr along with the surviving Elven warriors aided Roran in defeating the indomitable Lord Barst.