SAH asked an interesting question about case, I am [who/whom] G-d made me, but one issue that came up in the comments repeatedly is that many people said that they find the example sentence unacceptable with either pronoun.
This suggests that the sentence could be ungrammatical, but I'm having trouble figuring out why it would be. It is possible in general for the verb "make" to take a direct object and an object complement. The object complement can be an adjective, as in "They made me unhappy", or a noun phrase, as in "It made me a believer". We can say "It made me who I am", and things like "Your personality is what makes you you" or "These are the things that made me, me" (people seem to vary in how they punctuate sentences like these, but it's not that hard to find examples).
One thing I considered was that maybe it is grammatical, but hard to parse because it is a kind of "garden path sentence": many of the commenters expressed the idea that having both "who(m)" and "me" is redundant, which to me seems like a misunderstanding of the syntax of the sentence.
For example, Mitch said:
The relative pronoun should replace the subject or object in the relative clause but both are still there. It would be "I am who/whom G-d made" or "I am who made me".(who or whom both work; whom is hardly used at all in normal speech nowadays, but religious speech holds on to some archaism me like 'whom'.
[...] "X is who Y made Z" not grammatical. "Adjective is how Y made Z" grammatical (from "Y made Z Adjective") "X is who/whom Y loves" (from "Y loves X")
If the sentence is actually ungrammatical, and not just difficult to parse, it would seem to indicate some restriction on the ability of who or whom in this position to correspond to anything but a subject or direct object. I wonder if this is related to the dubious acceptability of "who(m)" in contexts like "the girl whom I gave the ring" (where many speakers feel a "to" has to be added to complete the sentence).
Surprisingly to me, it seems like there may be a difference between the animate wh-pronoun who(m) and the inanimate wh-pronoun what, since I received comments suggesting that similar sentences with what do sound acceptable to Araucaria and Mitch:
"What they named Christopher was the boy" doesn't seem to bear a good relation to the original, it seems to me . "What they named the boy was Christopher" seems ok to me ... (but grammaticality is in the ear of the beholder, no doubt!) – Araucaria
"What they named the boy was Christopher." sounds fine to me. Also "Christopher was what they named the boy" is fine too. – Mitch
In "Christopher was what they named the boy", the word "what" doesn't seem to be either a subject or a direct object, but nevertheless the sentence appears to be grammatical. So what's the relevant difference between this sentence and "I am who(m) G-d made me"?
I'm interested in knowing if there are any grammatical theories that explain why who(m) would be ungrammatical in this context, but any evidence (in addition to the already-established unacceptability judgements of a fair number of commenters here) that you can provide showing that the sentence with who(m) is ungrammatical would suffice as an answer to this question. (Or if you can show that the sentence is grammatical, that would also make a great answer!)