My list seems to be mostly antagonists... how odd. There are some spoilers in my reasoning so if you see a game you intend to play, skip it.
5. Reapers - Mass Effect seriesFor the first half of mass effect one, you hear the reapers mentioned a whole bunch, every time being dismissed as an ancient rumour. Saren, the game's primary antagonist appears to be bent on aiding their return. Then, you find yourself 'talking' with Sovereign, Saren's ship. Except it's not a ship. Sovereign, this colossal, cuttlefish looking motherfucker, IS a freaking reaper! Throughout the conversation, Sovereign reveals that the reapers have been annihilating intelligent life throughout the universe in a cycle spanning billions of years.
The reapers are everything you would expect ancient, sentient death machines to be. Cold, calculating, entirely emotionless and utterly terrifying.
4. Barney - Half-Life seriesBarney (along with all the other BMRF security guards) is just an all round good guy to have around. He's unquestionably loyal to his friends and knows how to hold his own when the situation calls for it. While not the smartest man in the world, he knows when it's time to fool around and poke fun at others and when it's time to man up and charge into combat.
3. Pagan Min - Far Cry 4Despite only seeing him in person a couple of times in game, Pagan's constant abuse and anecdotes over the radio makes him
one of my favourite antagonists in any game ever. I'm yet to finish the game so I don't know how things will turn out, but up to the points I am at he is perfectly unhinged and at times, utterly hilarious.
Some of his more hilarious moments are when he almost seems to mock various game mechanics in his rants, pointing out the ridiculous nature of the Far Cry series.
2. G-Man - Half-Life SeriesThis... thing is the reason the Half-Life story is so god damn intriguing. Despite appearing in 4 official games, we still no literally nothing about him. No clue as to whether he is even a genuine ally.
His involvement in Episode 2 really blows the lid off everything previously, not only revealing a huge chunk of answers but creating thousands of more questions.
1. Vaas Montenegro - Far Cry 3Vaas IS Far Cry 3. His "definition of insanity" was the first thing we saw at E3 when ubisoft revealed the game. Portrayed by and modelled after Micheal Mando, he was on the case art, he was on the posters, he was the star of all of the live action trailers and even had a live action mini series online.
He is completely insane, utterly terrifying to behold, and undeniably fascinating to watch.