The name Rhudaur appears to be dialect Sindarin for "Eastern Forests".
Rhudaur formed the eastern part of Arnor, and stretched from the Weather Hills with Weathertop (Amon Sûl) to the river Bruinen (Loudwater). It shared a long border with Cardolan along the Great East Road, and with Arthedain along the line of the Weather Hills.
The land between the rivers Hoarwell and Loudwater was also considered part of part of Rhudaur. It was called the Angle, and it is here that the first Stoor Hobbits came into Eriador around T.A. 1150. However, due to the increasing hostility of Angmar these Stoors fled the region around T.A. 1356, with some of them moving west to the Shire, and others moving back to Wilderland.
From the start of its existence, Rhudaur was unfriendly towards the two other successor states, and took part in a bitter conflict with Cardolan over the tower of Amon Sûl and the Palantír associated with the tower.
The last Kings of Rhudaur were not of Númenórean blood, but were descended of Men in service of Angmar. Under their rule the land became a vassal of Angmar, and thus enemies of Cardolan and Arthedain.
Angmar annexed and terminated the kingdom in T.A. 1409. By this time the Númenóreans were gone from the region, as well as most of the other inhabitants.
There is evidence that after the fall of Angmar at the Battle of Fornost the Angle became home to the remainder of the Dúnedain, and the Rangers of the North established several villages there, where their people lived until the resurrection of the northern Kingdom under King Elessar at the end of the third age.