Tales of the Mabinogion
Gwydion and Llew
Gwydion the hero had a son named Llew. Llew was married to the beautiful Blodeuwedd, who had been magically made for him from meadow sweet, broom blossoms, and oak. Blodeuwedd was unfaithful to Llew, and plotted to slay him with the aid of her lover, Gronw. Ah, but it is not easy to slay one who is the son of a god!
Llew could only be killed by a special spear if he was standing with one foot in a cauldron and the other foot upon a slain stag. Blodeuwedd tricked Llew into showing her the position, whereupon Gronw cast the spear. Llew turned into an eagle and flew far away. After a long search Gwydion found his son in Nantle (Caernarfonshire) and restored him to his human form with a magic wand. Gwydion then punished Blodeuwedd for her betrayal by changing her into an owl.
Maxen Wledig, Emperor of Rome
Maxen Wledig had a dream in which he beheld a beautiful maiden who sat upon a golden throne. When he awoke he sent his servants out far and wide, and eventually they found the maiden in Britain. The emperor hurried off to Caernarfon to woo and win the maiden for his wife. While he was absent from Rome his enemies siezed the throne. Maxen Wledig was able to regain power and defeat his foes with the help of his new wife and her friends.
More tales from the Mabinogion:
Olwen of the White Track
Pwyll and Rhiannon
Branwen invades Ireland
Manawyddan and the mouse