Galileo could be, let's say, prickly. “Look, he was a genius, and he was a truly unusual person, but he wasn't exactly nice,” astrophysicist and author Mario Livio, whose latest book is Galileo and the Science Deniers, said by phone. “He was nice to his family, he supported the members of his family ... and he had a few extremely good friends. But he could be nasty to his enemies. His sharp pen was just incredible.”