Countless ages ago a Celestial, whose true name is now forever lost to History, was murdered. By what it is not known but what is known is that it happened and the only evidence left of the crime is the Celestial's decapitated head which is slowly but surely riding the riptides of dying Universes towards the nothingness that lays beyond all of Creation.
It is believed that within the short span of a few decades Knowhere will be gone and all evidence of the murder itself will be lost.
The Space Station
Knowhere is used as a neutral base for many. It is governed by Gorani. The Head of Security is Cosmo. It is the base of operations for the Guardians of the Galaxy and the Luminals.
The station is massive and includes living quarters, medical facilities and a mainframe (known as the Continuum Cortex) that is extremely high tech, capable of instant teleportation.
Even though the Celestial is long dead, parts of it's mind still remain functional, as shown when Adam Warlock used the remainder to find the hidden Skrulls on board.
Following the events of The Inhuman/ Shi'ar Invasion of Knowhere, the long-dead Celestial has returned from the grave to deliver a message to Adam Warlock. The message was delivered from a alternate future from Starlord. All Celestials in all times are able to sense and communicate with one another. The message was that he is the only hope for the future.
Major Story Arcs
For more information see: Annihilation Conquest
The first comic book of Knowhere.
Knowhere is a peaceful place when the Luminals show up with the trapped Abyss. They plan to throw him into the end of the universe but he escapes, and turns some of the inhabitants into zombies. Nova shows up and with the help of Cosmo they are able to defeat Abyss and save Knowhere.
Realm of Kings
For more information see: Realm Of Kings
While chasing the Universal Church of Truth, Rocket Raccoon figures out how to pilot Knowhere, and take the head to them. This gives the Guardian and the Luminals the ability to rescue their friends and defeat their abductors. Afterwards Knowhere is returned to his original location.
For more information see: Secret Wars
In the Guardian's of Knowhere series, Knowhere is shown to be the moon that orbits Battleworld. In this reality, Knowhere is the head of a Celestial that came to collect Battleworld. It was slain in battle by God Emperor Doom and its head is still in orbit around Battleworld a reminder of his awesome power.
In Other Media
Knowhere appears in the post credits of Thor The Dark World, as the home of the Collector, although it isn't revealed to be Knowhere till Guardians of the Galaxy.
Knowhere appeared in the Marvel Studios film Guardians of the Galaxy (2014). It is home to the Collector, who stores his wide array of creatures and objects from around the universe, and his assistant Carina. The Collector also runs mining operations which mine tissue and brain fluid from the Celestial and sell on the black market.
Knowhere appears in the Guardians of the Galaxy TV series.