'Who' as a noun


Is it possible for the relative pronoun "who", which normally requires an antecedent noun/pronoun, to be used independently, or do we need to say "he who / the one who / the person who, as in:

1 - Who thinks he knows it all is deluded

2 - Beware who thinks he knows it all

3 - The most untrustworthy person is who thinks he knows it all

4 - Seeking the wisdom of who thinks he knows it all can lead to trouble

The sentences sound uncommon, if a little old-fashioned, but relatively okay to me. Or perhaps there's some Portuguese interference clouding my perception. I'm less confident about sentence (4) – using "who" right after a preposition somehow seems a bit odd, though in this sentence "whom" would certainly not be possible, despite the fact that "whom" can be followed by a verb, as in "This should interest my friends, most of whom are fond of reading."

Come to think of it, using "who" after a preposition may be actually totally harmless - a Google search offers countless examples of the type, "...Let's talk about who has freedom " ; "...keeping track of who is logged into..."; "...This change in who makes the news is also apparent..." (These sentences also seem to confirm that "who" does not need an antecedent; then again, Google searches are not always a very reliable source of grammatical sentences!)

I'm racking my brains, trying to remember in what kind of situation the use of "who" is not deemed grammatical, and it would have to be replaced with "whom". The only one I can think of right now is in sentences like, "The little boy at whom you're looking is an accomplished musician" .

Any comments would be much appreciated.

São Paulo, Brazil
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