('formal') The person to 'whom' we spoke to was very helpful. = ('formal') The person 'whom' we spoke to was very helpful. = (more commonly) The person 'who/that' we spoke to was very helpful.
('formal') Her brother, 'whom' I met last year, is an attorney. = (more commonly) Her brother, 'who' I met last year, is an attorney.
('formal') To 'whom' did you speak? = ('formal') 'Whom' did you speak to? = (more commonly) 'Who' did you speak to?
(..) She packed a bag. She packed a bag to go and stay with Mr. Quentin. Glenn Quentin, golf pro at the Snowden Hills Country Club... ...whom you had discovered was your wife 's lover. Did you follow her? I went to a few bars first. Later, I drove to his house to confront them. They weren't home. (..)1994 The Shawshank Redemption