Who in your eyes is the biggest traitor in Transformers history? Is it Starscream (G1) who tried time and time again to destroy Megatron, only to use his leader's demise at the hands of Optimus Prime to rise to power for 15 minutes? Was it Swindle (G1)? He did sell his fellow Combaticons as spare parts... Dinobot (BW) betrayed Megatron, almost betrayed the Maximals, then was killed. Came back as TM2 Dinobot, and ended up betraying the Predacons again at the end. There's Sideways in Armada, Demolisher and Inferno in Energon, Sideways and Soundwave in Cybertron... For me, personally, it's Rhinox. Rhinox was Optimus Primal's right-hand man in all of Beast Wars, and he was the first one discovered in Beast Machines ... as Tankor. And when they found him, Rhinox had concluded that Megatron had the right idea all along, that organics were a virus that had to be exterminated. Rhinox turned his back on the Maximals, on his friends and comrades, and tried to destroy them. It's like having a main character for 3 years suddenly turn traitor and then die as payment for his twisted principles. That was like "Woah" to me.