Sir Eider was born in Scotland in 880. Later in his life, he became the leader of The Clan McDuck. He is presumed to be the one who built Dismal Downs. In 946, the castle was under siege by Anglo-Saxons, raiders who didn't care about the treaty that King Edmund I of England and King Malcolm I of Scotland signed in 945. Sir Eider didn't supply arrows for his men and paid them only 30 pieces of copper an hour. His under-paid men abandoned the castle to save their lives and Sir Eider died fighting the raiders alone.
Sir Eider's descendants include Sir Quackly McDuck. Sir Eider was buried in the newly established family cemetery and his armor was placed in one of the castle's hallways.