Shrek is an enormous creature. He's incredibly strong, and he's tall even by the standards of ogres. It's a good job that he has such a big heart and a friendly personality, because if he didn't, we suspect he'd be a tyrant. It's not like anyone could stop him.
Ogres may or may not exist in real life. If they do, they probably look a little bit like Maurice Tillet. The brutish-looking man was a professional wrestler by the name of 'The French Angel' in the 1930s.