Samuel Johnson,
Notes to Shakespeare, Volume III: The Tragedies
“ I do not well understand how a man is reproached by being called zed, nor how Z is an unnecessary letter. Scarron compares his deformity to the shape of Z, and it may be a proper word of insult to a crook-backed man; but why should Gonerill's steward be crooked, unless the allusion be to his bending or cringing posture in the presence of his superiors. Perhaps it was written, thou whoreson C (for cuckold) thou unnecessary letter. C is a letter unnecessary in our alphabet, one of its two sounds being represented by S, and one by K. But all the copies concur in the common reading. ”
