Read this story from the first episode here.

Don Cuailnge, the Brown Bull of Cooley, was the target of Queen Maeve in the famous Cattle Raid of Cooley legend.  Maeve, the Queen of Connacht, had gotten into an argument with her husband about who had the most wealth.  When she came up one bull short, she decided to steal Don Cuailnge from the King of Ulster, touching off a massive war, which was the subject of the story.