X0-X1 was a prototype droid created by Doctor Issan Len. The droid was the result of Len's experiment to create a droid that could reprogram itself and eventually be able to manage the multifaceted systems of space stations.
In Cloud City on the planet of Bespin, Doctor Issan Len created X0-X1, but to program its artificial intelligence routines Len hired Doctor Vreen. Vreen, who was impressed by the droid's incredible technology, stole it in an effort to sell it to the Galactic Empire. Vreen then reprogrammed the droid to take control of Cloud City to turn it into a weapons platform. However, Vreen reprogramming caused X0-X1's functional stability to weaken and the droid instead started working towards its own goals. Vreen installed X0-X1 in the central computer core of Cloud City and with its new power X0-X1 developed Evolution Droids to help turn the organic population of Cloud City into metal-based automata, or "flesh droids", to do its bidding. XO-X1 quickly took control of Cloud City's droid population, then set them to work distributing the evolution droids around the city to transform the organic population. With its plan underway, X0-X1 started to plan the conquest of the known galaxy, as it now itself as the creator of a new, more evolved form of life.
X0-X1 was unable to complete its takeover because Vreen turned to a group of Alliance agents who confronted X0-X1. In a final desperate act, Walex Blissex shut down all of the power to Cloud City, effectively turning X0-X1 off as well. With the power shut down Cloud City's B/I repulsorlift engines no longer held up the city and it began to fall. Luckily, the Alliance agents were able to dismantle X0-X1 and reactivate the power to the engines before the city fell into Bespin's core.
X0-X1 resembled a large jellyfish with a flat disk as a central body and several steel tentacles.
- Crisis on Cloud City (First appearance)