Who is "The Man in the Red Coat" in the nonfiction book, The Man in the Red Coat?

Dr. Samuel Pozzi was a renowned surgeon, charismatic society man, unfaithful husband, and loving but distracted father. He was painted by John Singer Sargent in a portrait called "Dr. Pozzi at Home," in which he wears the infamous red coat and sexual pose which first inspired author Julian Barnes to research the dashing figure in the painting.