Star Trek: 12 Most Powerful Beings Ever
4. Nomad
Nomad was originally a probe that was launched from Earth in 2002, created by Dr. Jackson Roykirk. It's primary mission was to seek out interstellar life. However, early into its voyage, it was damaged by a meteorite. Then, it encountered the alien probe Tan Ru. The two merged to become the deadly probe.
Its mission altered to seeking out and sterilizing any life it deemed imperfect. Almost immediately prior to its discovery by the Enterprise, it wiped out four billion inhabitants of the Malurian System. Upon detecting the Enterprise, it began its mission again, firing on the ship in an attempt to sterilize it.
It halted its attack when contacted by Kirk, who it confused for its creator, Roykirk. It came aboard, detecting many imperfect lifeforms aboard. It wiped Uhura's mind and killed Scotty, though it was able to restore him with only a few moments of study required. It then gave the engines of the ship a dangerous power boost, to the point where the energy travelling through them threatened the ship itself.
Nomad discovered the co-ordinates to Earth in the ship's computers and set the Enterprise on a course directly to the planet. Knowing that it would sterelize Earth as it had done so many other creations, Kirk confronted it, causing it to grow confused once he pointed out that Nomad itself was imperfect, confusing him for its creator.
Nomad was so confused by this that it self-destructed, though Kirk was able to get it off the ship before it exploded.