The Scariest Alien Race Ever Imagined

In 1989, Star Trek: The Next Generation introduced us to the Borg, a collective of cyborgs that work together as one unit to capture and assimilate the universe's beings and technology for their own purpose- which is to capture and assimilate others. They are soulless, relentless, more powerful than Starfleet, and growing more powerful all the time. A truly frightening nemesis. 

In later episodes, the philosophical question of individualism, free will, and the hive mind are explored. However, over time and multiple appearances in later movies and series of the Star Trek universe, the Borg lost their horror because they were always ultimately thwarted. We also got to know a few individual Borg drones, and they became sympathetic. This video is 20 minutes long, but it's from The Art of Storytelling, so you know it's going to be riveting. (via Laughing Squid)