Rita Skeeter's smile flickered very slightly, but she hitched it back almost at once; she snapped open her crocodile-skin handbag, pulled out her Quick-Quotes Quill, and said, “How about giving me an interview about the Hagrid you know. Harry? The man behind the muscles? Your unlikely friendship and the reasons behind it. Would you call him a father substitute?”
I don't quite understand "The man behind the muscles". Does it mean: other than his muscles/power, what else does the man have? What does it mean exactly?