Harry Clement Stubbs, better known by the pen name Hal Clement, was an American writer and a leading figure of hard science fiction. A chemistry and astronomy teacher by profession, he applied his scientific rigor to his fiction, specializing in the creation of alien worlds and life forms governed by extreme but scientifically plausible physical laws. His most celebrated work is *Mission of Gravity* (1953), a novel emblematic of his approach, which describes life on a planet with exceptionally high gravity. His profound influence on science-based science fiction is also evident in other important works such as *Needle* (1950) and *Iceworld* (1953). For his fundamental contribution to the genre, in 1998 he was named a Grand Master by the Science Fiction and Fantasy Writers of America (SFWA), the highest career honor for a science fiction author.