Gareth Edwards (TES, February 13) should perhaps consider the following: “I am the man who met you” (in other words, I met you) and “I am the man whom you met” (or you met me).
He will then see that the object form of “who” is “whom” so “Who’s Whom” does not make sense. In the expression “Who’s Who” the copula - is - links the subject (the first “who”) with its complement (the second “who”), not an object.
Compare “I am a teacher”: “I” and “teacher” are one and the same person, not two different people, as in “I have a teacher”, where “teacher” is the object of “have”, a different person from the speaker, “I”.
Janet JV Kowalska
106 Spring Road
Letchworth Garden City Hertfordshire
