7. Robert Heinlein
Robert Anson Heinlein was an American sci-fi writer who is currently considered as the dean of sci-fi writers and he was the first sci-fi writer to enter the mainstream magazine publication. In his sci-fi works, Heinlein continuously incorporates a number of social themes, such as the tendency to repress non-conformist thoughts, the impact of organized religion on society, personal obligations to the society, self-reliance and individual freedom. He also addressed relationship between emotional and physical love and possible influences of space travel on human society. Throughout his career, Heinlein received four Hugo Awards.