The Krell are an alien race that has chased humans onto the planet Detritus and have been attacking them, attempting to keep the humans from gaining too much technology. The Krell are described as wearing bright colors, having red eyes, and looking like crabs. They seem to have a living apparatus with open plates of the "head" portion for them to see out of as a kind of armor. The Krell live in a space station near the planet Detritus, outside the debris field. This space station is shaped like a spinning top, with lights on all sides, appearing as a star at first glance. The Krell largly use Cytonics communication between themselves, but they will also use radios. Another form of Cytonics used by the Krell is a sort of mind control. They can take over the minds of some people and have them see things that are not there. This is what they did to Zeen Nightshade, making him see his allies as Krell ships, and shooting them. They attempt to do this to Spensa Nightshade when they encounter her. The Krell are very frightened of humans, not wanting to go near one because of how dangerous they are. They do want to study how the humans are building their ships, but when Spensa makes a face at them they flee from her, scared of what she will do.
The Krell have two known types of ship besides the space station. The first one is a ship of unclear purpose, but they might be couriers or tow ships. They look boxy, with large open windows in the front. On these ships is stenciled Ketos redgor Earthen listro listrins, translating roughly to Penitentiary maintenance and containment of Earthlings. The second type of this is the Krell interceptors. They are small, bulbous, with an unfinished look--with wires trailing behind like tails. They have small, opaque black cockpits, and will usually explode completely when damaged or when they crash. Inside the interceptors is Krell armor, dark forms in armor with red eyes, but the ships themselves are unmanned fighter drones.
The Krell are keeping the Humans on Detritus because the Krell were a part of a coalition of aliens that wanted the humans contained. The ship the Defiant refused to turn themselves in, thinking they were innocent. The Krell were sent to hunt down the humans, and cornered them on Detritus. The Krell keep them there for fear that if the humans escape they will try and conquer the universe. They do not see themselves as murderous, but as prison guards, trying to keep the humans from advancing too much. The Lifebusters were designed for this, and they attack frequently to keep human minds on defending instead of advancing their technology. They have laws against wiping out the human race entirely, and consider Detritus a preserve for humans. The Krell only allowed themselves to send a certain number of ships at once in attacks, for fear of accidentally causing humans to go extinct. The Krell aren't all on board with this plan, and the Second Battle of Alta really was meant to destroy humans, one faction having gotten it's way. 
Skyward · Starsight · Skyward 3 · Skyward 4
|Characters||Spensa (Spin) · Cobb · Jorgen (Jerkface) · M-Bot · Kimmalyn · FM · Rig · Hurl · Nedd · Arturo · Ironsides|
|Groups||Krell · Defiant League · Defiant Defense Force · Skyward Flight · First Citizens|
|Other||Detritus · Igneous Cavern · Alta Base · Flight School · Battle of Alta · Cytonics · Lifebuster|