Source: actionfigureinsider.com

4. The Manhunters

Look, first attempts are never the best. This is why we re-write things. The first draft, the pre-alpha, the first anything will always have a few bugs. Hence, the Manhunters.

The Guardians of the Universe decided millennia ago that the universe needed a police force. So they created a squad of robotic officers known as the Manhunters. Unfortunately, The Manhunters slowly realized that, hey, if all crime was emotionally motivated, and all sentient beings feel emotion, maybe the best way to fight crime was to KILL ALL SENTIENT BEINGS. You can probably see the problem here.

This led to tragedy when the Manhunters descended upon Space Sector 666 and killed everyone there, save five life forms. This was bad. This was real bad. The Guardians panicked, and destroyed as many of the Manhunters as they could find, but some escaped. The Guardians then created the Green Lantern Corps as a replacement.

This is a good idea because a. they could feel emotions; and b. they were not horrible freakish murder robots.