Who is the Welsh hero who sought the love of Olwen?

The Welsh hero who sought the love of Olwen was Culhwch.

Culhwch is the protagonist of Culhwch and Olwen, a Welsh tale preserved in the medieval manuscripts known collectively through the Mabinogion. He is a cousin of King Arthur and the son of Cilydd son of Celyddon and Goleuddydd.

Culhwch’s stepmother curses him so that he can marry no one except Olwen, the beautiful daughter of the giant Ysbaddaden Pencawr. Culhwch has never met Olwen, yet he sets out to find her and asks his cousin Arthur for help. Arthur sends warriors and magical allies to support the quest.

Ysbaddaden agrees to the marriage only if Culhwch completes a huge list of seemingly impossible tasks. These include rescuing Mabon, son of Modron, and helping capture the monstrous boar Twrch Trwyth. Culhwch and Arthur’s forces eventually succeed, Ysbaddaden is killed, and Culhwch marries Olwen.

The tale is more than a romance: its bridal-quest plot frames long catalogues of Arthurian heroes, supernatural beings, animals, weapons, and challenges.