From the pages of The White Goddess (Robert Graves, 1948), there is a legend of the battle between the Oak King and the Holly King. These two mighty rulers fight for supremacy as the Wheel of the Year turns each season. At the Winter Solstice, or Yule, the Oak King conquers the Holly King, and then reigns until Midsummer, or Litha. Once the Summer Solstice arrives, the Holly King returns to do battle with the old king, and defeats him. Read more about the story at About Religion.
The Oak & Holly Kings
by The Dolmen
The Colloquy of the Oak and Holly King
by Damh the Bard (website)