User blog comment:Daddy Danjer/Why need the Keepers if there is the catalyst??/@comment-108.23.19.253-20120813085205

The Catalyst did not create the Reapers. The rulers of the world or something like that realized that the conflict between organics and synthetics would go on forever, so they came up with a solution. They created the Catalyst, and sacrificed themselves to make the first reaper. Of course that isn't the full story, but it's the basics.