Widely considered one of the most influential and iconic writers of Sci Fi and Speculative Fiction of the Twentieth Century. He is counted as one of the "Big Three" of Science Fiction along with Arthur C. Clarke and Isaac Asimov. Often the standard to which other Science Fiction writers are compared, although he caught considerable flak for some of his recurring philosophical and political themes. His works range from space adventure YA novels to political manifestos, and generally score towards the "hard" side of Mohs Scale of Science Fiction Hardness.
Heinlein's most notorious and most dividing novel is Stranger in a Strange Land, an Author Tract which contributed hugely to the rise of the hippie movement. However, he's probably best known with the general public for penning Starship Troopers, which was very, very loosely adapted into a film.