Born in 2544 of the Third Age, he was the third king of Rohan, second son of Brego. His older brother Baldor was lost trying to use the Paths of the Dead. Aldor had four children, the first three were daughters, and his fourth was a boy named Fréa.

He came to the throne at a young age, 26, and was king for 75 years, the longest time any one king has reigned in Rohan. He lived to be 101, and this earned him the name of Aldor the Old.

Brego and Aldor rooted the Dunlendings out of the Riddermark and drove them beyond Isen. From then on the Dunlendings hated the Rohirrim, until they were appeased by the return of the king (Aragorn in the War of the Ring).

Aldor's reign was a successful one, and was a wonderful age for Rohan. Their numbers grew, and the Dunlendings were gone from their realm.