Harry Clement Stubbs, better known by the pen name Hal Clement, was an American science fiction writer and a leader of the hard science fiction subgenre. He also painted astronomically oriented artworks under the name George Richard.

Hard science fiction is a category of science fiction characterized by concern for scientific accuracy and logic. The term was first used in print in 1957 by P. Schuyler Miller in a review of John W. Campbell's Islands of Space in the November issue of Astounding Science Fiction. The complementary term soft science fiction, formed by analogy to the popular distinction between the "hard" (natural) and "soft" (social) sciences, first appeared in the late 1970s. Though there are examples generally considered as "hard" science fiction such as Isaac Asimov's Foundation series, built on mathematical sociology, science fiction critic Gary Westfahl argues that while neither term is part of a rigorous taxonomy, they are approximate ways of characterizing stories that reviewers and commentators have found useful.