Star Wars: Shattered Worlds
To the ancient Sith Lords of the era of the Mandalorian Wars, Korriban was their secret origin and host to their tombs and crypts (known as the Valley of the Sith Lords) and powerful Dark side powers learned from the ancient Sith race and perfected to bring them under their control. By the time of the first Sith Empire a great Sith Academy had been erected on the planet to train the armies of Sith that eventually conquered the Galaxy.
After the Republic eventually vanquished the first Sith Empire and vanquished their forces at their capitol world of Dromund Kaas, the remaining SIth retreated to Korriban and began to fight among themselves. Eventually, and the warring Sith Lords fell to Darth Bane, who reorganized the Order of Sith Lords under a new Code, the Rule of Two, designed to hide their continued existance from the Galaxy. To further this aim, records were altered and the planet became known as Moraband to keep its ancient secrets from the Jedi.
Eventually some of the Jedi learned of the nature of Moraband and the world was visited by Jedi Master Yoda in his quest for answers to the re-emergence of the Sith Lords. The world was also used by Darth Sidious to train his apprentices and various Dark side Force users under his New Order.
Korriban/Moraband was ultimately restored to its importance as the Sith homeworld when Darth Veritas gathered the leaders of remnant Sith cults long after the demise of Darth Sidious where they swore oaths and performed Dark side rituals to restore the Sith to power. His Dark Council set to restore the ruins of the thousand year old Sith Academy to a functioning training base, and by his decree restored Sith homeworld was to be known as New Korriban. There are currently several Sith acolytes and apprentices training at the New Korriban Academy.