1: He is no longer the person who he was ten years ago.
2: He is no longer the person that he was ten years ago.
Does the first sentence sound natural? Can "who" serve as a complement in a relative clause?
Thank you very much.
Both options listed by the original poster sound natural to my (American) ear. The "that" option sounds more natural to me than the "who" option. A third option would sound just as natural to me:
He is no longer the person he was ten years ago.
I would avoid the "who" option, because I try to avoid making choices between "who" and "whom". Choosing between "who" and "whom" interrupts my thoughts, both when speaking (or writing) a sentence, and when reading a sentence.
In other words, the choice between "who" and "whom" is consciously learned, not natural (in American English).
Yes, it can serve complement in a relative clause. And thus, both sentences are okay.
A sentence from the American Heritage Dictionary as mentioned in GrammarGirl
It is entirely acceptable to write either the man that wanted to talk to you, OR the man who wanted to talk to you.
The word that as a relative pronoun to mention a person has been quite common among authors.
However, I will go with GrammarGirl in this opinion of hers. It's interesting.
To me, using that when you are talking about a person makes them seem less than human. I always think of my friend who would only refer to his new stepmother as the woman that married my father. He was clearly trying to indicate his animosity and you wouldn't want to do that accidentally.