Betrayals are great plot motivators in video games. Or developers seem to think so, because at least one member of any given game's cast inevitably just hangs around on your side long enough to crap in your salad. A lot of betrayals don't make much sense. Or they come out of nowhere. Or worse still, they're so predictable that they the only one surprised is the moron protagonist. But every once in a while, a game comes along and pens an act of duplicity so daring that it manages to shake the foundations of everything you thought you knew. Here are seven such moments. Oh, and by the way:

7. StarCraft – Arcturus Mengsk

It's hard to peg Starcraft as sweeping epic of the human condition, what with the countless marines you so casually throw into the meat grinder just to delay an opponent's expansion. But the campaign of the first Starcraft painted a pretty bleak picture of advanced space-politics. The Confederacy has an iron-grip on human activity across dozens of planets. Even as two alien races emerge to challenge human dominance, colonial oppression runs deep. You turn to Arcturus Mengsk, a cunning strategist and master of oratory to liberate your species in the sector. Mengsk, his Lieutenant Sarah Kerrigan and the nameless commander controlled by the player are able to strike a few key victories against the Confederacy. But ol' Arcturus has a few more plans than just easing living conditions under Confederate rule. Manipulating the two new aliens, Mengsk wipes out an entire planet, leaving his second-in-command for dead in the process. After Mengsk's betrayal, no human force in the galaxy has the strength to challenge him. And after supplanting the Confederacy, his government proves to be just as intrusive and just as brutal.