The fact that they are all cooperating (to various levels) to beat back an outside threat does not make them friends (or even, in some cases, allies). In Harry Turtledove's Worldwar series, the various combatants fighting each other in World War II abruptly stop fighting each other and all turn their attention to fighting the alien invaders.And the moment they get the chance, the vampires betray Blade. They still don't like each other, and each side takes great pains to antagonize the other. In the second Blade film, the vampire hit squad teams up with Blade to stop the Reapers.The Predator's motive? He's still hunting the aliens, and hey, she proved herself useful in a fight and isn't an infected host so he may as well let her tag along if she wants to help him bag some more bugs. Predator film, Alexa Woods ends up teaming with the lone surviving Predator because she thinks it's the only way for her to get out of the situation alive (and she's right). In The Lord of the Rings: The Two Towers, the Ents help the people of the West by beating down Saruman not because they want to stop Sauron and destroy the ring (they specifically say that it's not their war), but because Saruman destroyed so many trees, and "A wizard should know better!".
![tv tropes avp extinction tv tropes avp extinction](https://i.ebayimg.com/images/g/NDQAAOSw4T1hql4L/s-l1600.jpg)
![tv tropes avp extinction tv tropes avp extinction](https://static.tvtropes.org/pmwiki/pub/images/79413ee2_02b5_41b5_86c4_bd645059294f.jpeg)
More like Hector needed them to advance his own agenda.
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This person is fighting the Big Bad, just like the hero, but is doing so on their own terms with their own agenda. The hero is working to stop the plans of the Big Bad Evil Overlord, and has, at long last, found an ally.