William Marshall (the man)
William Marshal (1146-1219) was a man who was barely even noble, but who rose to become one of the most powerful people in the Angevin world. His skill at arms was one source of his renown, being particularly successful at Tourney. He was the Marshal of England for a number of kings and fought in the Middle East as a Knight Templar. He is often held up to be a shining example of chivalry, but some historians claim that the evidence indicates that he was ruthless, pragmatic and manipulative. His son had a biographical text written L' Historie de Guillaume le Marechal.
William Marshal (event)
A Stormhold event held every year, usually on the first Saturday of December. It is in honour of William Marshall, the man. There is usually a chivalric weapons tourney, and a ransom melee followed by an elaborate feast with an early period theme. It is one of the two "high" events held annually in Stormhold, the other being Winter Feast.
It's the type of event that people who don't attend SCA events often come out of the woodwork for, and people wear try to wear their best garb, especially Angevin garb. It's just another excuse to make another piece of garb.