The Heechee are a fictional alien race from the science fiction works of Frederik Pohl. The Heechee are portrayed as an exceedingly advanced star-travelling race that explored Earth's solar system millennia ago and then disappeared without a trace before humankind began space exploration.
The Heechee first appeared in "The Merchants of Venus" (1972), a novella in the collection The Gold at the Starbow's End, sometimes called "The Merchants of Venus Underground". They also are referenced or appear in many of Pohl's novels and short stories published between 1977 and 2004.
Pohl's novels featuring the Heechee are:
- Gateway (1977)
- Beyond the Blue Event Horizon (1980)
- Heechee Rendezvous (1984)
- Annals of the Heechee (1987)
- The Boy Who Would Live Forever: A Novel of Gateway (2004)
Pohl has also released a collection of short stories in the series:
- The Gateway Trip (1990)
"The Merchants of Venus" 
The Heechee in fact originated as a plot device enabling Pohl to give a plausible reason for humans to make the effort of colonizing the inhospitable planet that space probes have proven Venus to be. In "The Merchants of Venus", the Heechee (a name given by humans since nobody knows what they called themselves) are nowhere to be found, and humans know of them only from their artifacts. The first evidence came with the discovery of tunnels constructed under Venusian surface, each tunnel distinguished by the mysterious cobalt blue metal covering the interior sections.
The tunnels facilitate colonization, since they can be adapted to human use at a fraction of what it would cost to dig them from scratch, and they and the other artifacts attract scientists who want to study them; then adventurers and prospectors who hope to make money by discovering more artifacts; and finally tourists rich enough to travel to Venus and see all this. By the next parts of the series, enough people have come to Venus to make it a sovereign state and a major power.
In the main part of the series, the frontier has moved away from Venus after explorers discovered an asteroid orbiting perpendicular to the ecliptic plane, filled with cobalt blue tunnels, and hundreds of small Heechee spaceships. The asteroid, named Gateway by the discoverers, is occupied by the powerful nations of the world, who subsequently form the Gateway Corporation to administer the object.
By happenstance, one of the asteroid explorers enters a ship and hits a button, activating the vehicle and sending him on a thirty-day journey to another solar system. Upon his return, the Gateway Corporation decides to allow explorers (called Prospectors) to take trips on the mostly still-functioning ships. Prospectors who find valuable materials or make discoveries are rewarded with substantial bonuses. Ships on the asteroids come in three sizes and are defined as a "one", "three", or "five" based upon the number of passengers that they can (for the most part uncomfortably) carry. Not every vehicle returns and there are other great hazards to the explorers.
The Gateway novel focuses on the exploits of one of those explorers, Robinette Broadhead. Broadhead hits the jackpot by becoming the first person to return from a black hole's event horizon. In the sequel, Broadhead uses the money to fund further discoveries involving Heechee technology, locating a Heechee food factory that is capable of turning raw carbon, hydrogen, oxygen and nitrogen (CHON) from comets into edible food for an overpopulated Earth.
The Heechee do not appear until book three in the series where the reason for their absence is explained. Some 500,000 years earlier, the Heechee were active in discovering the galaxy, including an Australopithecine-inhabited Earth (where a sampling of the creatures were extracted and left to propagate to modern time on a Heechee station). The Heechee found out that there was a race of pure energy called simply The Foe (or alternatively called either The Assassins or The Kugel) wiping out civilizations on any planet where they emerged. The inherently cautious Heechee retreated to the interior of the black hole in the Galactic Core hoping to avoid being destroyed. Due to time dilation, only a few hundred years have passed in the interior of the black hole since the Heechee left the universe. After going into hiding, Heechee scout ships are periodically sent outside the black hole to check on developments through the universe in general and the emerging Earth in particular.
When the latest Heechee crew exits the black hole, they are shocked to discover that humans are flying Heechee spaceships to all parts of the galaxy—and one of those places happens to be the Kugelblitz (a black hole made of energy and not matter), where The Foe was concentrated. The Heechee expected humans to discover the ships, but the cautious race believed Earth people would study and unlock the ships' secrets over a period of hundreds of years—and not simply take the equipment out for random rides in the dangerous galaxy.
When the Heechee finally arrive in force, it's decided that the human intrusion cannot be reversed and The Foe must be confronted.
The Heechee have collected evidence that The Foe have been adding matter into the universe. The Foe intend to tilt the balance and allow the Big Bang to be reversed and the universe to collapse into a Big Crunch billions of years into the future. The Foe intend that once the universe rebounds into a second big bang, it will do so in the form of pure energy, removing the atomic matter that The Foe regard as so much clutter. A détente is created between Broadhead and The Foe, allowing the aliens to continue their project and the human and Heechee growing to accept that they will eventually progress toward bodiless minds.
Physical and Cultural Attributes 
The Heechee's appearance is described as smaller than humans, bow-legged with skeletal frames, and possessed of dark, plastic-smooth skin with patches and curlicues of bright gold and scarlet. Each Heechee carries a microwave emitter in a storage pod between his or her legs. The pod is a trapezohedron shaped device and is also used for carrying equipment. The pods also explain why the seats on the ship have V-shaped indentations to accommodate the devices. The Heechee's home planet evolved near a naturally occurring microwave source, making the background radiation a necessary requirement for an ambient environment; the extended absence of the radiation will cause illness and death.
Heechee relationships do not generally feature couple cohabitation for lengthy periods as with human marriages. A burrowing species, they tend to display more solitary conduct than humans. A Heechee bed is a cocoon, stuffed with soft bits of fabric. Heechees only breed when a female is in season.
Heechee are vegetarians and use a fibrous plant to clean their teeth. There are two Heechee languages: the language of Do and the language of Feel, with communications with humans restricted to the former.
Unlike humans, the Heechee did not develop artificial intelligence. Instead, they relied upon technology to pour the brains of departed Heechee into data storage, giving them a limited immortality. These "stored minds" operate at remarkably faster speeds than "meat" brains. Those stored operate in their own social strata often separate from their organic counterparts. After centuries of existence, the various Heechee consciousnesses join the "massed minds", essentially dying while memories are distributed among other machine stored intelligences.
Heechee Devices 
In addition to the Food Factory, the Heechee created a number of devices that the Earth people discovered and used, including:
- Piezoelectric devices (allowing voltage to be generated from placing pressure on crystals).
- "Prayer fans" that appear and unfold like traditional fans but are actually computer-related equipment containing the minds of dead Heechees and, later, dead humans. The fans also are used for data storage.
- Faster-than-light spaceships that act by nullifying the mass of the ship and avoiding the implication of Einstein's Relativity Theory that states that an object becomes more massive as it approaches the speed of light.
- A Disruptor of Order in Aligned Systems is the device that allows Heechee to unseal the Schwarzschild barrier in black holes and allow ships to traverse the boundaries (referred to jokingly by humans as a "can opener").
- The "Dream Couch" or, more properly, a telempathic psychokinetic transceiver, is capable of receiving and transmitting thoughts across long distances. Heechees focus their law enforcement efforts on catching criminals while they are having perverse thoughts. In the novels, terrorists are depicted as putting insane people in Dream Couches and broadcast their thoughts into populated areas, causing widespread damage and destruction. Before learning of the Dream Couch being the cause, this was known on Earth as the "130-day fever", a period of planet-wide temporary insanity occurring roughly every one hundred and thirty days.
- Frederik Pohl at the Internet Speculative Fiction Database
- Review of Frederik Pohl's Gateway game
- Review of Gateway II game
- Heechee Saga at Worlds Without End