Who is Equitan's Seneschal from The Lais of Marie de France and what is their importance?

Equitan's Seneschal appears in Equitan. He is governor of Equitan's lands and the person who administers his kingdom. The king begins an affair with the seneschal's wife, and he narrowly escapes being killed by them when he discovers them together in bed. After the king dies in the trap he had set for the seneschal, the seneschal drowns his own wife in retribution.