The planet Vega One, more commonly called Vega or the Citadellian Homeworld was a planet in the Vega star system. It was colonized by the Citadellians, the race who founded the major space faring empire known as the Citadel. It had many moons, one of them which was called the Moon of Games. There were also several orbiting cities, and it was described as "the playground of the Intergalactic Underworld."
This world was originally a cold, barren world in a state of perpetual winter. Although the closest planet to Alpha Lyrae, it was protected from the blistering heat of the star by a thick layer of dust-like matter that absorbed energy and light, shielding the planet's surface. The First Citadellian chose this world because of its lack of natives and its harsh environment. This forced the Citadellians to adapt and survive or die.
Eventually the climate of the planet was changed to more favorable conditions, and many other races from across the galaxy began to come there. The Intergalactic Underworld used at least some of it as a recreational planet, where various criminals from throughout the galaxy that were members of the Intergalactic Underworld, could come to play games. Whether or not this was legal on Vega, or tolerated by the Citadel is uncertain, but it does likely give them commerce, giving support to their empire.