Ronan Coghlan has done a who's who on Grail Lore, with wonderful illustrations by Courtney Davis. Very readable, it lists all the characters surrounding Arthur and the myths and legends legends of the Knight of the Round Table. Coghlan is the Author of other useful books, Dictionary of Irish Myths and Legends and Irish Christian Names. Just not a list of people with a footnote of who they were, he fully references the listing with other writers of fiction and history. So not only is this a super reference to Grail lore is a good interface in history as well. It also covers places as well as people. Highly recommended for all Grail Library.
An excellent book in A-Z encyclopaedic format, dealing with all aspect of Arthurian lore. You can find out about Blaise, Elaine of Astalot and Camelot with ease. Lavishly illustrated too, with examples of great Arthurian art through the ages.