The Jester first appeared on the Denver RTG in August, 2061. It was activated by three deckers who stumbled into the Corp A host. Some background is neccessary.
Corp A had been doing research into a highly advanced 'smart agent' to assist with children learning the matrix. The origonal designer had been released from the corporation halfway through the project, and his code released to a team of 'corporate specialists' who obviously didn't have a clue of what they were doing. At the time the file was triggered, it's code was incomplete and did not have proper growth limiters installed, nor did it have a full personality suite to restrain its activities - but it did have all of the learning capabilities.
After the proto-AI lashed out, killing two of the deckers and heavily traumatizing the third, it began to grow at an exponential rate. Within two weeks, it had reached a size of over a hundred gigapulses, using it's ability to link it's code across multiple hosts to acheive such storage spaces.
Several Denver deckers encountered it in the Matrix and either came away by the skin of their teeth or received heavy psychotropic damage. Why psychotropic defenses were installed into the the system's code (made to help children) cannot be comprehended by our personnel.