Is Gareth Evans really a head of English? How can he suggest that "Who's Whom" is a more correct rendition of "Who's Who"?
The verb "to be" ("is") is intransitive: it takes a complement, not an object. "Whom" is in the accusative. "Who" is nominative and is used for the subject or for the complement of a sentence.
BA English language and mediaeval literature
Crumpsall Lane primary school