I definitely have a literality question that may never be answered, but I'm always looking for it!

Boy coming up with what to talk about today was a little hard when I got up this morning, but when I got to thinking about it I've had this question since I was eleven or maybe it was earlier than that as well. Here is the question, "When reading a book, where there are the good guys and bad guys and you know who is who but their is a third set of characters who are worse than even the bad guys, but at first the bad guys are teamed with those people, yet at some point in the story the bad side plays fair with the good side till the worse side is beaten/defeated? Where does this come from I'm just curious is all since I haven't been able to find the answer yet on my own. I was just watching a classic "Transformers" cartoon earlier today when it also hit me again for the millionth time what is the blasted answer? The Transformers episode was entitled "THE INSECITCON SYNDROME" which had the Decepticons looking for their Insections counterparts (Those could transform into bugs, where Decepticons transform into jets and weapons of mass destruction) to offer them a meal of energy instead of just forest trees to knack on, when really all the Decepticons want is to get a more easier way on a better way to get more energy for themselves. While the human friend Spike and the Autobots (these robots transform into cars, but fight on the side of goodness or hope, if you want to call it that) find out about the Insecitcons actions from a local forest ranger named Jeff. Come to learn of the plans the Insecticons do of the Decepticons while Soundwave a Decepticon records it all while they feast on the energy of the Nova power plant. The Insecticons make Soundwave their slave, Meanwhile the Autobots and Spike find out that the consumption of that energy isn't safe for the Insecticons and fight the Decepticons in a failing hope to have them understand how dangerous the Insecticons now are. Autobot scientists make a cure for the Insecticons only to barely save the plant with the help of the Decepticon leader Megatron. When in the end everyone still has to deal with the Insecticons no matter what side your on Decepticons or Autobots. I was just using a example here with a cartoon show, but like I said it also happens in literature very often too. Now I 'm not just looking for where the idea came from but my mother thinks it maybe in Greek writings or mythology, and I'm thinking maybe it is too but at the same time I want to know where the triple team up in literature started.....Maybe it's from as far back as biblical writings as well but there again I'm NOT sure....I just want to know if the internet would be of help, if I could only know how to search for it. But where do I start is what I know I don't have answers to.