Snape and Achilles Save the Day

The character Achilles reminded me of Snape from Harry Potter since they were both neutral until the end of the story and then they made a huge difference. In the stories both heroes died and they were supporting what they believed in. For Achilles he died for Sparta winning the war and for Snape it was fighting Voldemort and the death eaters so they wouldn't take over the world. The only difference was that Snape pretended to be the bad guy the whole time while Achilles never knew what side he was on until they killed his cousin.
   I think that the reason they have these people is that they need the good guys and bad guys to be going at it and it can't be clear on which side is winning until the end where a hidden hero comes out of nowhere and flips and side so the good guys have enough power to win.