Brainiac is the primary antagonist of the animated film Superman: Unbound. In this animated feature, Brainiac (voiced by John Noble) had sent out a series of robotic probes across the galaxy in search of new worlds with new knowledge to absorb. One such probe arrived on Earth where it was intercepted by Superman and destroyed before it could transmit to Brainiac's ship.
Superman learned of the robot's origin from his cousin Kara - Supergirl - who had witnessed Brainiac's menace first-hand when he had attacked Krypton years ago and took its capital city of Kandor. The only reason Brainiac hadn't outright destroyed Krypton then was because the planet was already approaching its natural end. Kara warns Superman of the threat Brainiac poses and the Man of Steel decides to intercept Brainiac and stop him before he comes anywhere near Earth.
Using a small Kryptonian rocket, Superman blasts off into space in search of Brainiac. He happens across an alien planet that is currently under attack by Brainiac and intervenes, destroying the villain's army of robots. However, Brainiac's ship then commences the abduction of the city Superman just saved, taking the hero with it. Brainiac then fires a solar aggression missile into the system's star, causing it to go nova and destroying the planet.
Superman awakes aboard Brainiac's ship where the villain analyses him, identifying him as Kryptonian. Brainiac then shrinks Superman down and deposits him inside Kandor, which remains miniaturised and contained aboard the ship with hundreds of other cities from different planets. Brainiac also reveals that he has learned of Earth's location from Superman's rocket. Unwilling to stand idly by, Superman, while held captive in Kandor, gets the attention of Brainiac's sentries by causing significant damage within the city. When the sentry robots appear to pacify Superman, he tears them apart and gets teleported back out of the city by the sentry retrieval system. Superman then causes as much damage as he can to Brainiac's ship before escaping and returning to Earth.
Brainiac does not remain adrift in space for long as his ship quickly repairs itself. He then proceeds on his way to Earth, appearing in the skies above Metropolis and deploying his army of robots to "sample" the human population. The military are unable to withstand the robot assault, but Superman and Supergirl return to Metropolis and destroy Brainiac's army. The two heroes find themselves aboard Brainiac's ship again when Brainiac abducts the whole of Metropolis. Brainiac reveals that he has no interest in Earth as he deems humanity as a primitive and weak species, stating that he plans to destroy Earth and even Metropolis after he's done analysing it.
Despite his efforts, Brainiac is unable to keep Superman confined. The Man of Steel breaks free of his restraints and releases Kara. The two of them then go about quickly dismantling Brainiac's horde of robots, but Brainiac then launches a missile at the sun in order to trigger a supernova. Supergirl goes after the missile while Superman battles it out with Brainiac himself.
Superman, believing that he has figured out how Brainiac's computerised mind works, hijacks the ship's teleporter and beams himself and Brainiac down to Earth's surface. The two end up in a swamp somewhere in the US and Brainiac is overwhelmed by the sensory input he receives: all of the different sounds and smells he experiences for dozens of miles around leave him disoriented and confused. Taking advantage of this weakness, Superman beats Brainiac into submission, sending him falling into the thick mud of the swamp. Brainiac, having never before left the sterile environment of his ship, is utterly overwhelmed by all of the new sensations around him and begins to malfunction. His cybernetic components go haywire and combust, melting the flesh off his mechanical skeleton which then collapses into burnt-out shards.
In a mid-credits scene, it is revealed that Superman salvaged Brainiac's remains and stored them in the Fortress of Solitude. However, the lights on Brainiac's CPU core suddenly come on, indicating that Brainiac may still be alive...