Science fiction is a vast and explorative genre of cinema. Anything can happen, and all so often anything does. When the possibilities are endless, there is a certain degree of expectation to keep going bigger than ever before, and that can clearly be seen in the villains of sci-fi films.
You're unlikely to find a dirty cop, a cheating husband or anything so small scale in films where you can go to other planets or travel in time. As a result, sci-fi is often responsible for a large assortment of infinitely powerful opponents that would be impossible to fathom in our own reality.
This power can come from various things; perhaps the villain in question has an excessive amount of strength; perhaps they're incredibly hard to kill; perhaps their power resides in their influence over others or the armies they control; perhaps they're proficient in killing or adept in adapting; and perhaps they are all of these things combined!
In a genre where anything can happen, the same goes for the antagonists of those very stories.
As sci-fi is increasingly varied in its approach, the villains on this list reflect just that. Some are geniuses, while some lack intelligence entirely - but all of them are hugely powerful entities within the genre.
10. Alien Queen - Aliens
After one Xenomorph proved to be a formidable threat to the crew of the Nostromo in the first Alien film, James Cameron upped the ante on both sides in Aliens as the Colonial Marines faced off against a horde of aliens spawned by the gigantic Alien Queen.
A huge and imposing creature, for the majority of the film the Alien Queen remains out of sight, laying countless eggs to add to her brood of murderous offspring. After Ripley torches those very same eggs, the Queen goes on a rampage as her maternal instincts kick in.
Stronger and more deadly than any Xenomorph previously faced, it is clear that even the well-trained marines would be ill-equipped to take on such a foe. In the end, Ripley has to work a mech-suit to overpower the terrorising threat and expel her into to space.
Xenomorphs have never been as physically dominant, or seemingly intelligent, before or since.