All right, let me preface this by saying that this is really more speculation than it is a theory, due to how much of this relies on things I made up. I also do not believe whatsoever that any part of this theory will be confirmed in the films, mostly because it's too complex for the movies to tackle. With mention of the mysterious "Creators" in Age of Extinction, it appeared that the continuity of the Transformers films was now damaged beyond repair. The discrepancies of the first three films had been successfully smoothed over in the IDW tie-in comics, but the revelation that the Transformers were created by an unknown alien race undercuts all of the history of the Cybertronians as told in the films. I believe, however, that the presence of the Creators (who appear, according to plot info, to be Quintessons), is actually the key to fixing the convoluted, contradictory continuity that is the Transformers films. A lot of the revised movie continuity I've described here is me interpreting some of the information we've gotten about TF5, as well as incorporating the presence of Unicron (and Primus, because at this point why not), and meshing it into the established movie continuity in an attempt to make all of this make sense. ***** In the beginning, there was Primus. Primus created life in the form of the Cybertronians, with the first of his creations being the seven Primes, who ruled as the Dynasty of Primes. Among the other races of Cybertronian included the Knights, an elite group of warrior-explorers, and the Seekers, who served under the Prime who would later be known as the Fallen. The Knights were led by Sentinel Prime, and included in their ranks were his successor-to-be Optimus Prime, the warriors who would be the Dinobots, and Megatron. Primus imbued his essence and life force into the AllSpark, which would continue to create life on Cybertron as the race thrived. Primus, however, had an opposite in the form of Unicron. Jealous of Primus's power to create the Cybertronians, Unicron attempted to create life of his own, but he could only create organic life. His creations were the Quintessons. Long after Primus defeated Unicron, the Quintessons and the Cybertronians remained in conflict. The Quintessons sought to revive their creator, and in the process they made use of "Seeds" of Unicron's essence to attempt to convert worlds into potential host bodies for Unicron. The Cybertronians, led by the Primes, fought to prevent Unicron's return. One member of the Dynasty eventually rebelled, seeing Unicron's resurrection as a means to gain power from the Dark God. Learning of the Quintesson's plans for Earth, he sent his Seekers to investigate the planet, and conspired with the Quintessons to use the Star Harvester and the AllSpark to advance their efforts to revive Unicron on Earth. The other Primes discovered the Fallen's treachery, and the ensuing War of the Primes resulted in the Fallen's imprisonment and the deaths of the rest of the Dynasty. This was, however, all a manipulation by the Quintessons in order to eliminate the leaders of the Cybertronians. Now without the Dynasty's leadership, the Quintessons defeated and conquered the Cybertronians. Using the powers derived from Unicron, the Quintessons reprogrammed the entire Cybertronian race to be used as a slave force. The AllSpark, which the Quintessons could not control or understand, remained on Cybertron. As time went on, however, the Cybertronians discoverd the AllSpark and rebelled against their masters, developing autonomy and a new civilization of their own. The Cybertronians developed a new belief system based around the AllSpark, which gave life to them and their planet. One Cybertronian, Sentinel Prime, was able to recall the ancient history of his race, and used that knowledge to his own ends by declaring himself Prime to gain leadership, along with his former Knights, Optimus and Megatron. From here on, everything plays out according to IDW continuity. Sentinel reveals to Optimus that he is a Prime (though still withholds all other information), Megatron is jealous and comes into contact with the Fallen who promises him power, the war between the Autobots and Decepticons kicks off, Sentinel Prime makes a deal with Megatron and escapes in the Ark, Optimus Prime sends the Allspark to Earth, etc. Now, fast-forward to Age of Extinction. The destruction of the Allspark/Cybertron's destruction has reactivated Unicron and the Quintessons. The Quintessons summon their agent, the factionless bounty hunter Lockdown, to capture and retrieve the remaining Knights. Lockdown succeeds in capturing the Dinobots, and by this time Megatron and Sentinel are dead, so Optimus is the last one. When in Lockdown's ship, Optimus discovers the Knights' Temenos, which contains the sword that he used as a Knight. When Optimus reclaims the sword, he regains his original memories, reformatting himself into his original form as a Knight. After defeating Galvatron, Optimus, now understanding who the enemy is and what they want, departs from Earth to face the "Creators." Now, as far as TF5 goes, we know a few things from the trailer and plot info. We know that Megatron is back in some capacity, either on his own or has changed from Galvatron. Megatron's new design looks suspiciously similar to Optimus's knight theme, right down to having a sword. We also see Megatron in the desert, as well as something that has crashed there. At the end of TF4, Galvatron appeared to escape in the Knight Ship. While on the ship, Galvatron discovered the Temenos and finds a sword of his own; when he picks up the sword, he regains his memories and is reformatted back into his Knight form, which explains his appearance and why he has returned to his original name. The plot details and rumors suggest that Unicron will be involved in some capacity, and most people seem to think that he's the moon-sized thing appearing to devour the moon in the trailer. My theory is that what we see is not entirely Unicron, but a fraction of Unicron (his head, spark, or something similar), which the Quintessons are bringing to Earth in order to fully revive Unicron. As for Optimus Prime, I know the two most popular theories are that a) he is reprogrammed by the Quintessons to help them, or b) the purple-eyed Prime we see fighting Bumblebee is an evil clone. Both of these options are compatible with my theory, but I lean toward the former just because it makes for a more interesting conflict if it's actually Optimus Prime and not just a copy. ***** tl;dr Transformers were created by Primus, but reprogrammed and enslaved by the Quintessons. Optimus regained his memories in AOE, and Megatron will do the same in TF5. Quintessons are trying to revive Unicron. All right, I think that about covers it. The whole thing is really more speculation than theory, and like I said I haven't the slightest hope that any of this will be confirmed by the film. This was mostly just me having fun trying to get the movie continuity to mesh together without blatantly contradicting anything in the films themselves, and I figured I'd type it all up and share it with you guys. If you read all this, I hope you got some enjoyment out of it. If you didn't, feel free to yell at me and tell me how stupid this is.