Hal Clement (real name: Harry Clement Stubbs) was an American ScienceFiction writer. Generally considered one of the [[MohsScaleOfScienceFictionHardness harder]] SF writers, he enjoyed creating unusual and extreme, but still realistic, settings and creatures for his stories. His best known works are ''Literature/MissionOfGravity'', about the inhabitants of an ''extremely'' massive planet, and ''Literature/{{Needle}}'', about a [[TheSymbiote symbiote]] detective who visits Earth in search of a symbiote criminal. All told, he wrote over a dozen novels and numerous short stories during his career. He was declared one of SF's [[DamonKnightMemorialGrandMasterAward Grand Masters]] in 1998.

Clement is credited with coining the term "symbiote"; the proper term in biology is "symbiont", but Clement's coinage caught on.
!! Tropes in his works:
* TheAggressiveDrugDealer: In ''Iceworld'', the protagonist is sent to infiltrate a criminal syndicate which has discovered a drug vapor that addicts those who inhale it with one dose. [[spoiler:The story takes place among aliens who live at very high temperatures, and the drug is tobacco, acquired via robot probe from a human who has no idea why the aliens are willing to trade gold for cigarettes.]]
* AllPlanetsAreEarthlike: Subverted by many of his works. Clement would go to great lengths to invent non-terrestrial planets and populate them with believable life forms.
* BabiesEverAfter: In ''Still River'', when they plan a return to the planetoid, a woman scientist observes that some of the aliens are coming out of curiosity in her pregnancy.
* BoldExplorer: In ''Mission of Gravity'', the small centipede-like creature named Barlennan on the planet Mesklin is a bold explorer, which is what brings him to the one area of the planet where humans can visit even briefly.
* EarthAllAlong: ''The Nitrogen Fix'' kicks this up a notch by making Earth ''actively uninhabitable'' to human beings (as in, survival domes and oxygen masks), and introducing an alien race that thrives in the new environment.
* The FairPlayWhodunnit: ''Needle'' is both a science fiction novel and a mystery novel. If you pay attention to the story and spot the clues, you can figure out the Fugitive's hiding place in the exact same way the Hunter does.
* FantasyWorldMap: Inverted in ''Mission of Gravity''. Clement created a globe of the planet Mesklin and wrote the story around it, but the book didn't include a map.
* GoodThingYouCanHeal: Handled consistently in ''Needle''. An symbiotic intelligent virus can heal many minor injuries and consistently defeat disease. Cue the protagonist getting careless about handling sharp objects, and nearly dying from an infection when the symbiote leaves.
* HeavyWorlder: The inhabitants of the planet Mesklin (which not only has high gravity, but a rather odd rotation) in ''Mission of Gravity'' are adjusted to this by looking somewhat like flat centipedes. The Mesklinites are the main characters of the story, which tells how a brave sea merchant retrieves a probe fallen from the sky for a strange space alien (i.e., a human).
* HollowWorld: Due to a combination of its gravitic and atmospheric oddities, the world of Mesklin in ''Mission of Gravity'' was thought by its inhabitants to be bowl-shaped. They were incorrect (it was actually a very flattened spheroid).
* HumansThroughAlienEyes: A trope found in many of his works:
** ''Needle'' has an alien detective getting a crash course in humanity so he can try to find the bad alien, who is hiding out on Earth, without revealing his own existence.
** ''Mission of Gravity'' gives us a view of humanity from an alien centipede who is terrified of heights greater than a few centimeters. The humans' insistence on standing upright seems dangerously insane.
** ''Iceworld'' is told from the point of view of aliens who find Earth be be dangerously cold.
** The front cover blurb for ''Cycle of Fire'' invoked this with the words: "Each of them was a stranger to the other. But which was the alien?"
* ProudMerchantRace: The Mesklinites in '' A Mission of Gravity''
* SpaceIsCold: Inverted in-universe "Sun Spot". 'Grumpy' Ries has to spend a couple hours keeping an astronomical camera, and its operator, from getting cooked on the surface of a comet making a ''very'' close pass by the Sun. When he comes back inside, the observatory's doctor offers to treat him for burns. Ries points out he's been manhandling sacks of frozen methane and other ices which were still at the temperature of interstellar space. "Break out the frostbite remedy, will you, please?"
* TheSymbiote: The detective-creature in ''Needle'' and ''Through The Eye Of The Needle'' was a blob of protoplasm that entered a human host to survive and move around-bordered versions two and three, because the boy was not harmed at first but then became ill in the second book. There was also another creature, the hunted fugitive, who'd taken another body and was a PuppeteerParasite type.
* TechnologyMarchesOn: In ''Mission of Gravity'' and ''Star Light'' (as in 'not heavy'), the humans in the stations orbiting the supermassive "Terrestrial" type planets Mesklin and Dhrawn use slide rules. "Star Light" was published in 1970.
* UnderwaterCity: Handled as realistically as possible in the short story "Ocean on Top". A colony of humans is established on the ocean floor, using geothermal power to provide light and a specially-made oxygen-carrying dive fluid in place of air. But since the humans are less dense than water, the humans have to wear weights if they want to stay on the bottom or even have neutral buoyancy. They sleep tied to the ceilings of their buildings.
* WaterIsAir: Averted when a colony of humans is established on the ocean floor, using geothermal power to provide light and a specially-made oxygen-carrying dive fluid in place of air. But since the dive fluid is denser than water, the humans have to wear weights if they want to stay on the bottom or even have neutral buoyancy (their bones were denser than the fluid and their lungs were filled with it, but the rest of their bodies were less dense and the net effect was a slight positive bouyancy). They sleep tied to the ceilings of their buildings.
** Played with in ''Close to Critical''. The planet Tenebra has atmospheric conditions close to the critical point of water. This leads to some truly bizarre effects like large blobs of water hovering in the air, and people lighting fires to drive water away at night.
* WorldShapes: Mesklin in ''Mission of Gravity'' spins so rapidly that it's lens-shaped rather than spherical. Except at the equator, however, the atmosphere is so dense due to the planet's intense gravity that refraction makes it look bowl-shaped. The Mesklinites can "see" that the world curves up around them, so they believe that they live in a giant bowl. They are skilled sailors and map-makers and should know better, however when you are measuring distances on a curved surface, there are two different shapes that will make all the math work out (convex and concave). The Mesklinites choose the wrong one for their maps and never notice. The result is perfectly accurate and usable maps based on a fundamentally flawed premise.