Three entries with the name Gilbert.
Gilbert
Son of Cadgyffro and one of Arthur’s warriors and advisors in Welsh legend. A Welsh Triad lists him as one of the Three Slaughter-Blocks of the Island of Britain.
He rode a horse named Red Wolf-Tread who is listed as one of the Three Chief Steeds of the Island of Britain.
Sources
Triads of the Island of Britain (Welsh ”Triads”) | 11th century to 14th century
Breudwyt Rhonabwy | 13th century
Gilbert
The valiant son of Tjofabier of Merkanie, slain in his father’s war against Gerhart of Riviers. He was avenged by Arthur’s knight Sir Garel.
Source
Garel von dem blühenden Tal | Der Pleier, 1240-1270
Gilbert
Gylbart, Gylbert
Father of a maiden upon whom Gawaine begot a child in The Jeaste of Sir Gawain.
When Gilbert learned that Gawaine had slept with his daughter, he challenged him to combat and was defeated, as were his three sons, Gyamoure, Tyrry, and Brandelis.
He is known as Norrois in the first continuation of Chrétien’s Perceval.
Source
The Jeaste of Sir Gawayne | Late 15th century
Note
The name Gilbert is Norman, and was borne by several British rulers in the twelfth century; the particular progenitor of the name was likely Gilbert of Clare (1243-1295), Earl of Gloucester.