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).
Charles Williams (British writer)
Although Williams attracted the attention and admiration of some of the most notable writers of his day, including T. S. Eliot and W. H. Auden, his greatest admirer was probably C. S. Lewis, whose novel "That Hideous Strength" (1945) has been regarded as partially inspired by his acquaintance with both the man and his novels and poems. Williams came to know Lewis after reading Lewis's then-recently published study "The Allegory of Love"; he was so impressed he jotted down a letter of congratulation and dropped it in the mail. Coincidentally, Lewis had just finished reading Williams's novel "The Place of the Lion" and had written a similar note of congratulation. The letters crossed in the mail and led to an enduring and fruitful friendship.