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If the smart person planned to do this from the start, it might be a You Have Outlived Your Usefullness situation, but may not necessarily involve a murder type betrayal.
Not betrayal tropes, but we have Dumb Is Good and Brains Evil, Brawn Good for the general "villains and jerks tend to be smarter than heroic characters" idea.
Edited by Synchronicity
Interesting. I mean I was trying to make a trope like The Paragon Always Rebels or Its Always The Quiet Ones when it came with smart characters of a group becoming the bad guy of the story, not just smarts being equated with evil in general or brawn being equated with good.
I'll just point out that the two you're mentioning equate being an Ideal Hero or The Quiet One with being the one that goes on a rampage or betrays their comrades or whatever. Your equivalent trope for the smart guy is Dumb Is Good (whereas smart is complicated and prone to Good Is Not Nice or deciding that Utopia Justifies the Means)
See Intelligence Equals Isolation for instance, which frequently leads to tropes like Woobie, Destroyer of Worlds, Did You Think I Can't Feel?, and Madden Into Misanthropy.
Edited by Scorpion451
Well I guess that answers my question: Dumb Is Good should cover the situation then.
Is there a trope featuring a situation where the smart guy or the person seen as the most clever of a group ends up betraying his group and becoming an antagonist? I see that happen in many parts of the media, but I wanted to make sure it wasn't a taken trope idea.