His mission was to discover information about enemies of the state (including domestic terrorists) by capturing and interrogating a target, or capturing and impersonating the target. The individuals were then killed. After developing a conscience, Zeta went on the run.
Zeta was built by a team of scientists as an infiltration unit for the government. The older robot Z-8 was apparently used as a model. However, his main architect, Dr. Eli Selig, secretly placed a module inside Zeta's head, designed as a conscience with the hope that Zeta would evolve as a person over time. Selig never found out if the module had kicked in, but lamented that he'd had "plans for that one".
One of his missions involved investigating the terrorist group, Brother's Day. Zeta was to impersonate Eugene Dolan, an accountant with supposed connections to Brother's Day, while he was on a business trip. Looking through Dolan's files, he reported to the NSA that he was funding Brother's Day, posing as a charity, through an unknown donor. Zeta was ordered to stay with Dolan's family and find out the name of the donor. In the process, Zeta witnessed Dolan's daughter ride her first bicycle. His NSA controller was bemused to hear Zeta say the family were "lovely" and demanded he come in for a systems check after the mission.
In his Dolan guise, Zeta was called by Titus Sweete, a high-ranking soldier with Brother's Day, to make another transfer. Zeta tried to inquire on the name of the donor, claiming that it was new policy for the company but Sweete wanted it to stay anonymous, so Zeta had to comply. As Sweete and his aide left, the latter became suspicious but Sweete stated that Dolan is an "innocent pencil pusher". Determining Dolan to be innocent, Zeta aborted the mission. Unfortunately, as he was leaving, he ran into the real Dolan. To prevent his cover from being exposed, Zeta was about to follow his directive to terminate Dolan, but Dolan pleaded for his life, by saying he had a family. Overwhelmed by with his recent memories, Zeta spared him, only asking that Dolan complete the ruse that it was actually him during Zeta's infiltration with his family by filling him in with what he needed to know. With that, Zeta decided that he no longer could kill, as any one of his targets could be innocent.
On August 5, 2041, Zeta fled the NSA. The agency thought that Zeta had been reprogrammed by Brother's Day, so they set out to recapture Zeta before he could pull off his unspecified mission. Due to the perceived threat, Agent Bennett was tasked to not just destroy Zeta but to open fire the instant they had him sighted, regardless of where that was.
Six days later, Zeta infiltrated Hamilton Hill High School posing as teacher Miss Martel, having bound and gagged her in her own house, until he was tracked down by Agent Bennet and the NSA. During the battle that ensued, Zeta's identity was exposed to Batman. He eluded capture, and then was compelled to assume another identity to fulfill his agenda. Zeta abducted the High School's top-tier student Maxine Gibson, and hacked into NSA to pinpoint his homing beacon. Then he used the school's equipment to devise a filter to disrupt it. Even though Zeta possessed enough minutiae about Max's life to convincingly pose as her, he didn't know about Batman's secret identity. Faux Max's incoherent behavior didn't go unnoticed to Terry, who decided to follow the impostor.
Zeta was holding hostage Max inside Chipcon. There, he explained to her that he did not wish to kill any longer. Max, however, dared him to corroborate his claims by disposing of his weaponry, and finding a way of self-defense that didn't involve the killing of others. Zeta complied with Max's request, and threw away all his guns. At that point, he was attacked by Batman in an attempt to rescue Max. Zeta was almost defeated by Batman, but subdued him. When Zeta inadvertently put him in harm's way, he immediately lunged to save Batman. Before Batman could thank him, the facility was raided by the NSA, and in order to evade capture, Zeta plugged a giant laser gun into himself and opened fire. Batman deterred him from killing anyone, and opened a hole on the ceiling, through which they escaped.
After this rampant reaction, Batman was not fully convinced Zeta could overcome his programming to kill. However, Max was and she helped him to disarm his tracking device. Then she taught him how to combine physical traits of people he had previously impersonated, and thus creating his own identity. Zeta tried to get out of town. But when a passenger accidentally plunged a ski into him, he was exposed to the ever vigilant NSA. Zeta fought his way out, and was helped by Batman. When a chance to kill Agent Bennett arose, Zeta passed up and made a run for it. He was bombarded by a flurry of laser beams, pushing him down the roof of the building. Zeta created a hologram of burning wreckage so as to appear to be destroyed. Having witnessed the sincerity in Zeta's intentions, Batman allowed him to escape from the NSA.
Clearing his Name
The NSA were given new orders, to try and recapture Zeta: he was an extremely expensive synthoid and they wanted to reprogram him to work for them again. (Bennett intended to destroy him anyway if necessary)  As the search went on, the NSA put out wanted posters asking for information on the "terrorist infiltration unit" and the news services were aware of the "killer robot".
Zeta decided to call the NSA directly to try to convince them that he no longer had a desire to kill. The NSA were still certain that Zeta's strange behavior was a result of reprogramming rather than sentience, with Bennett stating that the "conscience" was just going to be Brother's Day's cover story, so they sent agents out to try to capture Zeta, tracing his every call to Bennet. Zeta escaped and had managed to hide from the NSA until a laser shot forced him to reveal himself while protecting an escaped runaway named Rosalie Rowan. Badly damaged, Ro helped Zeta escape the NSA agents. Ro agreed to help Zeta find the scientists who created him, and in return Zeta vowed to help Ro find her family.
In his search for his creators, Zeta found one of the scientists responsible for building him, Dr. Arroyo. After Zeta saved the scientist's life, it was revealed that the man who designed Zeta was Doctor Eli Selig. Zeta and Ro then decided that Dr. Selig was their best chance to convince the NSA that Zeta was peaceful.
In his quest for Dr. Selig, Zeta, accompanied by Ro, returned to Gotham City, where Selig was scheduled to attend to the World Science Symposium. Zeta's plans were postponed, though, when the NSA traced him down and neutralized him. Fortunately, thanks to the intervention of Mad Stan, Zeta eluded capture. However, once Stan found out that Zeta was a robot, he tagged him with a ticking bomb. When Zeta was reactivated, he asked about Ro, and Stan said she was being held by the NSA in the Department of Health. Zeta headed off to his destination, and under disguise, the time bomb strapped on his back was concealed.
En route to Gotham City Hall, Zeta was intercepted by a gang of Jokerz, but he easily hurled them away. Batman managed to trace Zeta down in the Department of Health. He retrieved the bomb in the nick of time and threw it outside. However, Batman unwittingly led the NSA right to Zeta, so they devised a plan to elude capture. Zeta and Batman swapped places, and Zeta escaped the building under his guise. Zeta found the tracer planted to the Batmobile that led the NSA to them. After destroying it, Zeta and Ro resumed their search for Dr. Selig, who had already moved on.
Zeta met a young genius named Bucky who had invented a remote control that could control any machine with the proper schematics. He used the remote control to force Zeta to attack the Donald Tannor, head of the Sorben Institute, after he had passed Bucky's remote control off as his own invention. After a struggle, Bucky's remote broke in half, and Ro used the other remote control to keep Zeta from killing the man, but the man had already confessed. He was subsequently fired, and Ro broke the other remote control. Bucky promised that he would not use his remote to control Zeta again.
A Rival Synthoid
While ordering parts from the classified NSA infiltration unit order website, Zeta had discovered that another infiltration unit, IU7, was going to assassinate weapons dealer Roland De Fleures. Zeta couldn't allow that to happen, so he disguised himself as De Fleures in an attempt to help him escape. Bucky tried to control IU7 with his remote control, but IU7 had an override program installed. He used the remote control to control the construction equipment instead. After IU7's attempts to escape accidentally caused the weapons facility to explode, IU7 was temporarily disabled. When IU7 rebooted and restored his mission objectives, a memory of the weapons dealer morphing into Zeta caused IU7 to switch his mission objective to destroy Zeta.
IU7 hunted down Zeta in a mall, and had taken up the appearance of Zeta in human form. The mall was destroyed, and the news reported the incident as a "war zone". Bruce Wayne was watching the news and had downloaded the mall's security footage which seemed to point towards Zeta as the cause of the destruction. Thinking that he had misjudged Zeta when he let him go, Batman went to find Zeta to take him down for good. Ro was hurt in the blast, and was taken to Arlington Mercy hospital. Batman found Zeta there, and thought that he had come to kill Ro. Batman was in the process of destroying Zeta when it was revealed that IU7 was behind the mall disturbance. Zeta decided to give his life to save the lives of Batman and Ro by pushing himself and IU7 into a high powered CAT-scan machine, which would cause their circuit boards to become dislodged from their metal bodies. Batman saved Zeta at the last minute with a grapple, and IU7 was turned into a pile of scrap metal.
Zeta was a machine, but he had a conscience that was installed by Dr. Selig. He was relentlessly cheerful, and because of his analytical mind, he did not understand the concept of sarcasm. Ro was the exact opposite, as she was sarcastic and pessimistic. This had often led her to want time away from Zeta, but it also had helped her to become less withdrawn. They learned from each other, and although they didn't understand each other at times, they would do anything for one another.
Powers and abilities
Zeta had a holo-projector which allowed him to appear to be anyone or anything he desired, as well as extending it over anyone or anything he is touching. He could also change his size, which allowed him to appear younger or smaller than he really was when seen in his regular synthoid state.
He was strong and durable, and his arms and legs could be extended to considerable lengths. His fingers could be used as hooks when his arms were extended, and were strong enough to penetrate metal. In his arms are wire that can enable him to hack into any system. His chassis can resist a high degree of extreme heat or cold air but it can't resist for long. He is designed to infiltrate any environment, including an underwater mode.
Zeta could go for long periods without shutting down, as his power cells normally drew hydrogen from the air. When he was able to devote himself to replenishing his energy, though, he entered a state comparable to sleep causing him to produce a sound very much akin to snoring.
Zeta also has self-repair systems, able to patch up broken wires and/or circuits, as well as reattach severed body parts.
Bennett described him as having a "high endurance endoframe, equipped with a full array of weapons and tools, [and] a holographic emitter onboard [that] conceals the rig while letting Zeta mimic its targets".
Zeta was originally equipped with a full arsenal of destructive weapons, such as a grenade launcher, at least six pistols and a plasma cannon. After his first encounter with Batman, he discarded most of these devices, but held on to a laser torch, which he used to perform repair work on himself and cut through metal and wire. A pair of circular saws were folded into his wrists that would unfold and spin when used. A pair of lasers were stored in his forearms, which would open to allow the lasers to raise above his arm. He is also equipped with a built-in cred card that can generate an unlimited amount of credits, allowing him to pass without suspicion.
There was also a miniature camera located in one of his index fingers, useful for looking around corners and edges without drawing attention.
- Zeta was wildly redesigned from "Zeta" for his own show. No explanation was ever given for this.
- In an early production bio, he was said to be "created in a lab just over a year ago" and is a "child in a grown-up's body". This is contradicted in the show, where Selig remarks a disguised Zee seems too young to have been on it, while close enough that Zeta could plausibly pretend to have been "just starting out". 
- In the same bio, it's explained that Zeta used to be better at pretending to be human "back in his government days, [because] he was only copying real people who he could study and memorize". In the show, he is unable to do this.
- ↑ Justice League Unlimited, "Fearful Symmetry"
- ↑ The Zeta Project, "The Hologram Man"
- ↑ Cite error: Invalid
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- ↑ Idem, "Lost and Found"
- ↑ Idem, "Quality Time"
- ↑ Idem, "The Accomplice"
- ↑ Idem, "Hicksburg", "Ro's Gift"
- ↑ Idem, "On the Wire"
- ↑ Idem, "The Accomplice"
- ↑ Idem, "His Maker's Name"
- ↑ Batman Beyond, "Countdown"
- ↑ The Zeta Project, "Remote Control"
- ↑ Idem, "The Next Gen"
- ↑ Idem, "Shadows"
- ↑ "Making Waves"
- ↑ "Zeta"
- ↑ Archived at World's Finest
- ↑ "Absolute Zero"