The Ka Luon are grey humanoid creatures with long limbs and large black eyes who match the common description of the alien type known as "grays". These creatures have large mobile Chantries that look like space ships. The Ka Luon and Zigg'raugglurr are two possible alien races that lead the Void Engineers to try and establish a network of worldwide Horizon Constructs.
The Ka Luon figure heavily in the Ascension scenario "A Whimper, Not a Bang". In this scenario, the Ka Luon are resisting the activities of the Zigg who seem to be draining reality of its Avatars and by extension magick and Dynamism which may spell the end of their advanced technology.
The Ka Luon were first attracted to human activity shortly after World War II. They've been engaged in a war with the Border Corps, or at least that's what the Void Engineers believe. The entities known as the Psychopomps are purported to sometimes appear like them based on the current Sleeper expectation that that's what an alien thing looks like.
The Void Engineers also appear to have a common enemy in the Ka Luon with the Zigg'raugglurr.
Sources support the Ka Luon being both materialized spirits conforming to the expectations of Sleepers as well as being proper aliens from space. The capstone book Ascension lists them as being aliens, but a sidebar provides that someone may not wish this to be the case.
The Ka Luon always appear to be materialized when encountered in the Umbra and have access to what seems to be exceptional technology.