9999999999999999999999999 was first conceptualized by Chuck Norris, who invented it in his sleep. It was then brought into existence by the Flying Spaghetti Monster, which apparently has the ability to do such a thing. Then, 9999999999999999999999999 moved to Number Island, and the Flying Spaghetti Monster disappeared, never to be seen again (in the UnUniverse, at least).
9999999999999999999999999 has been simplified to just OVER 9000, which is its current name. It is often used to descibe the power level of Chuck Norris, but is not even remotely close to Chuck Norris' true power level. It is stated to be OVER 9000 as shown by Vegeta.