Many people will try to fool you into believing that Robert A. Heinlein is the dean of science fiction. He isn't. This 'title' was awarded by the SF community to someone who was already writing SF in the 1920s when Heinlein (whose writing career began in 1939) probably didn't even know what science fiction was all about, and it was given to him mainly because he simply was the oldest Golden Age SF writer alive most of the time.

The Dean of science fiction has always been, is and will remain Murray Leinster.

'Nuff said.