St. Swithun was a bishop of Winchester. He was a performer of miracles. One story tells that he saw a poor woman on her way to market with a basket of eggs. She bumped into a monk and all her eggs were broken. St. Swithun took pity upon her and made the eggs whole again.
Although Merlin correctly describes Swithun as still living by 800 AD, he refers to him as a "Saint". While Swithun is a Saint of the Church, it is a title that is given only to people who are in Heaven so normally he wouldn't refer as such to a current living person.