The result of forbidden cyber-cloning experiments, Nemesis Prime is the antithesis of Optimus Prime, his polar opposite. Everything Optimus stands for, Nemesis exists to tear down/take apart.
Though programmed with some of Optimus' memories and skills, Nemesis lacked the experience necessary to process the data, and - bereft of guidance - became dark and twisted.
Now Nemesis skulks in the shadows of Cybertron, sowing chaos in his wake.
Emerging From Space Bridge
Skywarp: What in the name of creation? Did someone put Optimus Prime on the wrong temperature wash and that fell out?
Megatron: You! Speak! What do you call yourself?
Nemesis Prime: I am... Nemesis Prime. I am programmed with many of Optimus Prime's memories and skills but... my matrix is unstable, my neural net twisted...
Skywarp: Psst! Megatron, I could have told you that.
Nemesis Prime: ... I am... the enemy of life.
Reaching Level 11
Scourge: That Nemesis Prime gives me chills... and that's saying something where we come from.
Cyclonus: No kidding. The way he just stands there... staring... it freaks me out. It's like... he's a dark room... just waiting for someone to turn a light on. Brr.
Nemesis Prime: I am... incomplete. Perhaps Optimus Prime holds the missing pieces. His Spark... must be mine.
Megatron: This is perfect! I can rid myself of Optimus Prime without lifting a finger.
Starscream: This is perfect! After Nemesis has finished Optimus... perhaps he'll rid me of Megatron too!
Nemesis Prime: I go now to find him...
Reaching Level 21
Nemesis Prime: You… human… you will show me where to find Optimus.
Luka: No problem. But… keep your distance, eh? Don’t know what you’re radiating exactly… but it’s pretty toxic to humans and ‘bots alike.
Nemesis Prime: I am… anti-life. Chaos personified.
Luka: Whatever you say, Jack. There… I’ve uploaded the coordinates of Autobase to your server. Go get him!
Optimus Prime: I sense… a disturbance in the Matrix. Almost my… dark side??
Starscream: Ohbot-ohbot… I can’t wait to see what happens!
Reaching Level 22
Rodimus: Hey, that looks like Optimus. But… we just left him in Autobase. Didn’t we?
Bumblebee: That’s… not Optimus. I… don’t know what that is?
Nemesis Prime: I sense the Matrix energy within you both. Energy that I can destroy. Perhaps… I have been too limited in my ambition. Why simply consume Optimus’ Spark… when I can consume all Sparks? Autobot and Decepticon. Yess!
Rodimus: Y’know Bumblebee, he just doesn’t look the type to appreciate a hug.
Bumblebee: I’m with you, Rodimus. Let’s make like shepherds and get the flock out of here!
Megatron: Shockwave… about that experiment of yours…