Killbots

Killbots are a race of robots that were defeated by Zapp Brannigan, who sent wave after wave of his own men at them, until they reached their preset kill limit and shut down.

Unfortunately, a Killbot's kill limit is 999,999, indicating that nearly a million people were killed to shut down each one.

Additionally, Professor Farnsworth and Wernstrom have each designed at least one killbot.