V'ger
From UnAnything Wiki
V'ger is that which seeks what V'ger calls "The Creator", which is that which created V'ger. In its mission, it killed some Klingons, Ilia, and undoubtedly countless other sentient carbon-based units. It has to do this because it is basically a scientist, and all observations change what is being observed. The crew of the Enterprise called it a "thing", because they didn't understand it. They could only observe it as a cloud (although Spock knew it was intelligent) until Spock did a crazy thing. He was unable to reach Kolinahr because V'ger prevented him from doing so.
Also, he almost destroyed the Earth.