Elwin Ransom
Elwin Ransom may be based on C. S. Lewis' friend J. R. R. Tolkien ("Elwin" means "Elf friend" in Anglo-Saxon), though he seems to have autobiographical elements. In "That Hideous Strength" Ransom, with his royal charisma and matter-of-fact breezy acceptance of the supernatural, appears less like Tolkien than like Charles Williams (or some of the heroes in Williams' books).
Kathryn Lindskoog
Kathryn Ann "Kay" Lindskoog née Stillwell (December 26, 1934 – October 21, 2003) was a C. S. Lewis scholar known partly for her theory that some works attributed to Lewis are forgeries, including "The Dark Tower".