This is one of the good people in the story. He was Tom’s master in New Orleans. Also, he seems to be a very rich and romantic man. He started loving and being fond of Tom after the last saved his daughter in the river when she started drowning. St. Clare is an unstable man looking for faith, and Tom tries to help him. Why we love Tom and Augustine more? Because St. Clare promises Tom his freedom! Can you imagine this in those times? Unfortunately, he is killed in a bar before he can sign all the papers.
Augustine St. Clare in the Essays