Tankor
Background
In the followup to the Beast Wars series called Beast Machines, the Maximals return to Cybertron to find a changed world. Missing two of their own (Silverbolt and Rhinox), unable to transform, and having no recollection of what has transpired since the time they left prehistoric Earth, they were caught wholly unprepared for what awaited them. Cybertron was a barren planet, ruled by Megatron, the leader of the rogue Predacons they had fought during the Beast Wars. His ideal of technological purity for Cybertron was enforced at first by legions of mindless Vehicon drones but later by three generals designed to control the drones: Jetstorm, Thrust, and Tankor. To Tankor fell the task of commanding the tank drones.
The Basics
It would be a massive understatement to say that Tankor was not exactly the sharpest knife in the drawer. Fortunately for Tankor, the forces of stereotyping were on his side, so he possessed quite a bit of strength. Next to Megatron, he was the largest and strongest of the Vehicons. As his name might imply, he transformed into a tank. Neither Jetstorm nor Thrust particularly cared for him. Yeah, it would seem as if Tankor was a pretty boring guy...after all, he was just this big bruiser who wandered around Cybertron hitting people and yelling "TANKOR SMAAAAAAAASH." Of course, when dealing with Transformers, there's always -- oh my god, am I really about to say this? -- more than meets the eye.
During a diversionary battle with Tankor, the Maximal Rattrap was able to patch into his processor and access his memories. He then made a startling discovery: their enemy Tankor was in fact their long-lost friend Rhinox. Well, maybe that's not entirely correct; Tankor possessed the corrupted spark of Rhinox. After this discovery was made, however, it served only to confuse and disorient Tankor. And when Tankor gets confused and disoriented, he likes to blow things up. Needless to say, this didn't put our heroes in a very good situation. Worse still, when Optimus Primal was able to contact Rhinox's spark, he turned away from his former friend and commander, claiming he had "abandoned" him. When the slow-witted Tankor personality eventually subsided entirely, the Maximals met a very different Rhinox. Not only did he not want to rejoin his comrades, he enthusiastically endorsed Megatron's plan of organic genocide, saying, "Megatron is the only hope this planet has!"
"Goodbye, old friend."
As a Maximal, Rhinox had been something of a polymath. He could repair just about anything. He could design all sorts of weapons and other devices. He was a great admirer of the natural beauty of prehistoric Earth. He was also a total badass. He wielded double machine guns and shot the hell out of anyone dumb enough to walk in front of him during battle. In general, however, Rhinox was soft-spoken and very loyal to his friends and fellow Maximals. This was no longer the case. The new Rhinox was jaded, manipulative, contemptuous of everything organic, and very ambitious. Although he was a proponent of Megatron's mission to technologically purify Cybertron, he saw Megatron as being wholly unfit to rule over it. Although Megatron's plan might have looked good on paper, there was one fatal flaw with it: Megatron himself was still partly organic. He never lost his beast mode after returning to Cybertron. To Rhinox, this disqualified his ability to rule over a perfectly technological Cybertron. Is it any wonder who Rhinox/Tankor believed ought to rule in Megatron's stead?
Beyond Redemption
Tankor faked his own death and reprogrammed Megatron's diagnostic drone to serve only him. Tankor eventually discovered the key to Vector Sigma, the super-computer that gave all Cybertronians life. This is significant because the key was able to turn organic matter into purely technological matter and Cybertron was somewhat "infested" (in Megatron's words) with organic matter. Through the diagnostic drone, Tankor convinced Megatron to make replicas of the key and outfit the Vehicon drones with them. That way, they could deploy a massive blast of matter-changing energy directly into the somewhat organic core of Cybertron and eradicate all traces of organic matter from the planet. Likewise, the organic Maximals would have been turned wholly technological should they be hit by the energy. This applied to the partly organic Megatron as well. Tankor played both sides against each other, trying to destroy Megatron and the Maximals in one fell swoop. Although it was easy for him to prey on the emotions of the Maximals (Optimus Primal in particular), Megatron was not so easily baited. Frustrated with Megatron's caution, Tankor revealed himself and attempted to destroy both of his former commanders. There was a problem, however: Megatron's programming never vacated the premises of Tankor's processor. One such bit of programming prevented him from harming his master, Megatron. Megatron then revealed that he had granted Tankor autonomy and had planned for his betrayal all along, hoping to reap the benefits of whatever "discoveries" he might have made on his own, such as the Key to Vector Sigma. Tankor was then summarily destroyed.
Optimus Primal met Rhinox within the Matrix during his tenure in a state of limbo. Rhinox told Primal that although he had made the wrong choices in life, there was still time for Primal to go back and pursue the path of techno-organic harmony on Cybertron. And with that, he was gone forever.
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