Who or whom?
There’s a continuing debate in English usage about when you should use who and when to use whom. According to the rules of formal grammar, who should be used in the subject position in a sentence, while whom should be used in the object position, and also after a preposition. For example:
You can read more about the rules and guidelines about when to use who and when to use whom on the Oxford Dictionaries blog. Here you will find tips on using who and whom as relative pronouns and useful tips on how to get it right in writing and in speech.