Glewlwyd Gafaelfawr; "Brave Grey Mighty Grasp," is a hero, warrior and porter in tradition and Arthurian mythology, in which he appears as a knight in Arthur's retinue and chief gatekeeper of his court. He is one of the earliest characters to be associated with Arthur and appears in a number of texts, including Culhwch ac Olwen, Geraint fab Erbin, Iarlles y Ffynnon, Pa Gur yv y Porthur and the Welsh Triads.
After being cursed by his stepmother such that he may marry no one but Olwen, daughter of the giant Ysbaddaden, Culhwch ap Cilydd seeks assistance from his cousin Arthur to win her hand in marriage. He arrives at his court at Celliwig but is denied by the Glewlwyd, the chief porter. Culhwch threatens to wreak havoc unless he is granted entry to the court and, eventually, Glewlwyd relents. In a bombastic speech given in this tale, Glewlwyd recounts his history to Arthur, in which he claims to have been in different exotic locations across the world and Otherworld, often alongside Arthur:
This passage is closely related to the narrative of the tenth-century poem Pa Gur yv y Porthaur; "What man is the porter," in which Glewlwyd is the titular gatekeeper of fortress to which Arthur and his men are seeking admittance. To prove their right of entry Arthur relates the feats and achievements of his men; particularly those of Cai and Bedwyr.
Later on in Culhwch ac Olwen, Glewlwyd leads his servants during the hunt for the man-turned-boar, Twrch Trwyth, and three of them, Huandaw, Gogigwr and Penpingion, are killed in the process, mortally wounded by the quarry. Glewlwyd is left with Llaesgymyn, "a man who was no use to anyone" as his sole remaining servant.