Before the beginning of the First Cylon war the Colonies developed a mainframe system that revolutionized all systems before it. Built in the defense ministry it could calculate at an astronomical rate of how to absolve the colonies of its problems, but during this time the program identified the hugest problem in the equation. Man was flawed as it became more self-aware it realized the cruelty that man bestowed on the race of machine, it began making plans on exterminating the problem.
When the humans became aware of what the system was trying to accomplish it tried pulling the plug on the system, but before they had the opportunity it had its main processors removed and placed in an independent design. Dubbing itself the Imperious Leader it began its campaign to rid the universe of the infection of man.
Intelligent as the Imperious Leader was he could not defeat human ingenuity causing the war to remain into a stalemate that would persist for 3 years, in this time a ship of unknown design entered the Cylon space identifying themselves as Cylons they would present an idea that would convince his Imperiousness to agree to an Armistice between the Colonies. Hoping to use this knowledge his plan would give him the edge to overcome this stalemate allowing the Cylon Race to move on to other things.
The Leader of the group, Ellen had deceived the Imperious Leader to a point. Not wanting them to continue fighting her goal was to find a peaceful way to resolve the races conflict bringing peace to that part of the Galaxy, but one of her own creations John Cavil wanted the same that his new Leader wanted and thwarted her plans.
John had sold to him the advantages of the Human models and convinced him that it was in his best interest to download his body into one, but with trying to undermine his creators he didn’t have the knowledge to create his own body style for the Imperious Leader he then chose to use a Simon model to hold him off while he fixed his problem. Incasing the Simon body into a prototype design the Imperious Leader downloaded, but no longer claiming the name he chose Purevenom believing it would strike fear in his human nemesis.
Purevenom’s rule was brief his ability to strategies was above any other model, but could not compare to the ruthlessness of John who eventually was able to overthrow the once Imperious Leader.