The Cybock Imperium was a group that was considered a threat to the universe.
After defeating the Hyperions, Rassilon and the Alliance of Races embarked on another campaign against threats to universal harmony. One such enemy was Count D'if of the Cybock Imperium. Rassilon challenged D'if to a game of Rassilon's roulette using the Time-Gun of Rassilon. D'if lost and he was wiped from existence.
In 1962, some surviving members of the Cybock Imperium, led by Commander Kronos, relocated to Las Vegas and formed the secretive Kronos Family. They steadily expanded their criminal empire over the space of one year, often by seizing assets from the Dragotta Family.
In 1963, the Cybock Imperium stole the Time-Gun of Rassilon from a vault on Janizzar. After Clara Oswald managed to recover the weapon, the Twelfth Doctor challenged Kronos to a game of Rassilon's roulette and won. Kronos' timeline was erased, and so was all involvement the Cybock Imperium had ever had with Earth. (COMIC: Gangland)
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