Well, according to the manual, the Stream Riders of MDK fame grind entire planets down with their Mine Crawlers, so assuming a successful empire...they have been ending civilizations for a longass time.
Even then, I can probably top it with Deus Ex machina from Xenogears. It is a massive galactic destruction weapon system complete with core body and enhancements, a personal attack vessel, armies of mechs, and planet-shattering power. What it was doing prior to being packed up on the Eldridge is up to debate, but it was probably not good. And it didn't help that it killed nearly everyone ON the Eldridge and then proceeded to create and genocide a human-like race for about 10,000 years to generate and create enough living components to repair himself. (This last bit was done IN HIS SLEEP.)