0 (Currently) / Unknown (Formerly)
None (Currently) / Magnus the Red (Formerly)
Prospero was the original homeworld of the Thousand Sons Traitor Legion of Chaos Space Marines and their Primarch Magnus the Red. It was a center of knowledge and lore, particularly knowledge of sorcery and the Warp before its surface and its planetary capital of Tizca were scoured by the planetary assault of the Space Wolves Space Marine Legion at the start of the Horus Heresy in the early 31st Millennium. This assault was arranged by the Warmaster Horus, who sought to turn the Astartes Legions against one another and to drive the Thousand Sons into the arms of Chaos so that they would support his own attempt to overthrow the Emperor of Mankind. After the Space Wolves' assault, Prospero was declared a Dead World by the Imperium, like all of the former homeworlds of the Traitor Legions.
Chosen by its settlers for the planet's isolated position although it still remained far closer to Terra than many other human colonies settled during the Dark Age of Technology, the Civilised World of Prospero had only a few redeeming qualities. It possessed no independent resources, little contact with any outsiders and only a few sources of nourishment. The only reason for planting a colony there was because it was a very good place to hide, and thus became a large community of psychically talented and often physically mutated humans who could find no refuge elsewhere in the galaxy.
During the Great Crusade, Prospero had developed into a paradise world. Many of the vast buildings on the planet were massive gold and marble pyramids. Prospero was a planet with blue skies and gleaming Egyptianesque architecture. One of the world's many cities was the capital city of Tizca, often referred to as the City of Light, where the Thousand Sons later held out against the Space Wolves when they were mistakenly declared traitors against the Imperium.
Prospero's "cleansing" at the hands of the Space Wolves was hastened by the dilapidated state of the planetary defenses. As the homeworld of a Space Marine Legion, it was standard for the surface of such a planet to be protected by immense planetary Defense Lasers sunk into reinforced silos many miles beneath its settlements. Orbital fire platforms, automated tracking stations, minefields, as well as a number of the Legion's own starships -- all were manned continuously and diligently.
The focus of the Thousand Sons, having always been away from the traditional Space Marine role of combat, and in most forms towards the use of sorcery and psychic abilities. This had led to a dangerous weakening of the Prosperan defense grid. The cavernous subterranean defense lasers were neglected, unmanned and poorly maintained and the orbital defenses were virtually non-existent. As a result, the arrival of the Space Wolves' Battle Barges went uncontested, their orbit-to-surface ordnance barrages unanswered and their drop-pods unchallenged.
Ironically, whilst the attack was underway, the Thousand Sons' focus remained on their lore – rushing to save what incalculably precious works of sorcery and psychic research they could whilst the righteous, if possibly misplaced retribution of Leman Russ' Legion went unchallenged. Indeed, had a defense of Prospero been attempted, more time might have been bought to evacuate the libraries and studies of their ultimately costly work.
The planet was transformed into a blasted ruin, picked clean by millennia of looters and Rogue Traders, after an Exterminatus was unleashed upon it by the Imperium after the Horus Heresy because of its connection to the Thousand Sons and its people's heretical sorcerous heritage. Such a fate befell each of the homeworlds of the Traitor Legions, since each was believed to be a source of Chaotic corruption that could not be cleansed save by utter annihilation.
Prospero is the main protagonist and master sorcerer in William Shakespeare's The Tempest. It is also a satellite of the gas giant Uranus in the Sol System.