who was captain beatty?

Here is a good analysis:

"Beatty is a complex character, full of contradictions. He is a book burner with a vast knowledge of literature, someone who obviously cared passionately about books at some point. It is important to note that Beatty’s entire speech to Montag describing the history of the firemen is strangely ambivalent, containing tones of irony, sarcasm, passion, and regret, all at once. Beatty calls books treacherous weapons, yet he uses his own book learning to manipulate Montag mercilessly."