Knight of the Spring, Knight of the Tower
The lord of the Giant’s Tower, also called the Knight of the Tower or the Knight of the Spring, after the Spring of Healing which ran near his fortress.
He guarded the Spring and fought any knight who came his way. Although he was often less powerful than his opponent, he won the combats because he know the secret of the Spring of Healing. In this manner, he defeated and imprisoned Gawaine, Gaheris, Bleoberis, and Sagramore.
He was finally defeated by Palamedes during the Grail Quest, and he was forced to free his prisoners, although Palamedes allowed him to continue guarding the Spring.
Source
Post-Vulgate Queste del Saint Graal | 1230-1240