10. Lavos - Chrono Trigger
Lavos crash-landed on the planet millions of years before humanity existed, with the sole intention of draining the Earth's energy to produce genetically enhanced spawn, that could carry out the same attacks elsewhere. Lavos actually slept for millions of years whilst it gathered power, until it awakened ready to cause an apocalypse. In Chrono Cross, Lavos is revealed to be responsible for the creation of the modern human species.
9. GLaDOS - Portal
GLaDOS, is an artificial intelligence created by Aperture Science that was your only means of contact throughout the original Portal, helping to guide you through the tests that laid before you. She would often resort to psychologically abusing the player, guaranteeing cake that didn't exist and forcing you to incinerate your companion cube, after you have likely become very attached to it, as well as constantly lying to you throughout the entire game.
8. Albert Wesker - Resident Evil
Throughout Resident Evil, it was clear that there was a traitor in the S.T.A.R.S team, but it was not until the end of the game that it was revealed to be Albert Wesker, your team leader. Although he seemed dead at the end of the first game, he actually infected himself with the T-virus, becoming more deadly with each appearance he makes, aiding his plan to infect the world with the deadly virus.
7. Bowser - Super Mario Bros
Bowser is the King of the Koopas who wishes to kidnap Princess Peach from Mario and marry her, before completely conquering the Mushroom Kingdom. No matter how many times Mario rescued Princess Peach from Bowser's many castles, Bowser would always return to kidnap her again, along with his many children who were all as equally villainous as him.
6. The Joker - Arkham Asylum / Arkham City
The Joker needs no introduction, he has been Batman's greatest enemy since their creation and holds everything in the world as a joke, taking nothing seriously, especially when it comes to sending his countless goons to face Batman knowing full well they will only get beaten. Joker's insane plans and vicious disregard for anything and anyone, seemingly including himself, guaranteed him a place on this list.