Sowhoandwhomarerelativepronounsthatrepresent a personwithin a relativeclause, whetheritisthesubjectortheobjectwhocanalwaysbeused?
Forexample, thepersonwholivesupstairsisverynoisy.
That's a subject.
ButJohn's theguywhoyoumetyesterdaythatanobjectjustlikeinthequestionwhomistheobjectformofwho, in a relativeclause, itrepresents a personthatistheobjectofthatrelativeclause.
Again, it's mostlyformalandmostlyusedin a writtenstyle.
Forexample, thepersonwhom I spoketodeniedmakinganynoiseagain.