The Heechee are 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'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 exponentially 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.

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 Heechee were just approaching the threshold level of FTL activity when they discovered the Assassins and decided to build a sophisticated cloaking system to hide the advanced state of their civilization, of four shield generators designed to create a 'blind spot' of warped space around the WatchTower. The shields were located on Delta Aurigae 6, Kaduna 3, Psi Dorma 5 and Nemira 3.

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.