Years ago, Emperor Palpatine chose the world as his private retreat, and Imperial architects and engineers were commissioned to build him an opulent palace. Several million humans per month, lured by the rumors of a paradise planet, were allowed to emigrate to Byss-- where the Emperor and his Dark Side Adepts began feeding off their life energies. The planet's population reached almost 20 billion, and all outgoing communications were censored by security agents. Byss was well-guarded against attack with powerful planetary shields, hunter-killer probots, and the Imperial Hyperspace Security Net, and contained orbital drydocks for the massive World Devastators and the more recent Galaxy Gun. The Imperial control sector covered most of one continent, and Palpatine's kilometers-high Imperial Citadel could be found at its center. The vast Citadel contained gardens, museums, the Emperor's Clone Labs, barracks for Imperial troopers, and a fully-equipped dungeon; it was guarded by advanced turbolasers and dangerous monsters called "Chrysalides" or Chrysalis Beasts. Certain freight haulers were specially licensed to ship to the protected Deep Core, where they delivered their cargoes to the heavily-defended Imperial Freight Complex. The Freight Complex, on the outskirts of the Emperor's ruling city, was three kilometers wide, nearly 168 kilometers high, and was tethered to an orbital satellite for added stability. It contained a popular spacers' hangout known as the Byss Bistro.
Following the Battle of Endor, Grand Vizier Sate Pestage was impeached and stripped of
authority by those who feared he might claim the title of Emperor for himself. Pestage retreated to
Byss, where he prepared for Palpatine's expected return. The Emperor did indeed manage to
survive his "death" at Endor, and his spirit returned to Byss to inhabit a new clone body.
Weakened by the difficult journey, Palpatine convalesced on Byss for years before finally taking
his revenge against the New Republic six years after the Battle of Endor. During this period, Luke
Skywalker attempted to learn the secrets of the Dark Side as the Emperor's apprentice after a
Mandalorian prison ship delivered him to Byss. Later that year, Lando Calrissian and Wedge
Antilles led an unsuccessful attack on the Imperial Citadel using a cargo of hijacked Viper
Automadon battle droids. Soon after, in a battle near Onderon, Han Solo and a team of
commandos hijacked the Emperor's flagship Eclipse II and brought it through hyperspace to
Byss. R2-D2 steered the Eclipse II on a collision course with the Galaxy Gun, which accidentally
fired a planet-destroying missile into Byss' core, utterly destroying the Emperor's throneworld.