I'm not a fan of Charles Williams, but Grevel Lindop's biography of him, Charles Williams:The Third Inkling, has been widely praised, even winning a Mythopoeic award for Inklings Studies last year. About the only criticism of Lindop's book I've seen concerned it's name. Tolkien scholar David Bratman, for example, has argued that calling CW "the third Inkling" unfairly puts CW into the shadow of Lewis and Tolkien, whereas people interested enough in CW to read a biography of him would undoubtedly rank him higher.
Thus I was startled to see a reference by Sorina Higgens in her edition of CW's verse drama, The Chapel of the Thorn, to Lindop's then-unpublished biograph: Charles Williams: The Last Magician.
Off the top of my head, I suppose the name change came very late in the process, probably at the instigation of the publisher. A title linking CW to the Inklings, rather than to the occult, would probably sell a lot more copies. In terms of Lindop's own take on Williams, though, the "Magician" title indicates where Lindop's greater interests lay. As many have noted, the Inklings section in the biography is relatively brief, although it's hard to fault Lindop for that since Williams joined the Inklings pretty late in his life.
For my part, I was okay with The Third Inkling as a title, but the fact that it was apparently bestowed so late in the process is, I think, highly illuminating. I still have very little sympathy with any writer so fascinated in the occult, but Lindop's work certainly gave me a better appreciation of what Williams was trying to do.