re: Dawn of the Planet of the Apes (Thoughts with Spoilers; Fricking fantastic)

I felt Koba's personality was established within the first few seconds he appeared in rise. He is clearly an overly aggressive alpha beyond what rocket was in rise. He is only loyal to Caesar because Caesar freed him from who he hates the most. When Jacobs watches koba spelling his name and then staring back at him it's pretty clear

Also Caesar lets his dog off the leash so to speak when he allows him to kill Jacobs. He's an unstable psychopath and the rediscovery of humans sets him off again. It also presents an opportunity to get revenge and usurp Caesar

His behavior after the first sighting is usurpacious whereas before he seems to be adjusting well

Long story short: the sight of humans triggered a psychotic break