When first referring to an author, use his or her full name; thereafter, use the last name. (For example, although you may feel a real kinship with Robert Frost, you will appear disrespectful if you refer to him as Robert.)
With characters’ names, use the literary work as a guide. Because "Bartleby, the Scrivener" always refers to its characters as Bartleby, Turkey, and Nippers, so should you. But because "The Management of Grief" refers to Judith Templeton either by her full name or by her first name, it would be odd and confusing to call her Templeton.