The Triceratons are an alien race who resemble anthropomorphic triceratops, and usually breathe a mix of nitrogen and sulfur. Outside of their native environments, they usually wear protective face helmets to provide them with necessary atmosphere. They destroyed their home planet for some unexplained reason.
Some TMNT stuff was always meant for grownups.
Along with the Fugitoid, the Triceratons were one of the earliest creations of Mirage Studios, predating the TMNT. In the minds of their neighbors, they are really an empire that covers the entire central region of the Milky Way Galaxy, a huge interstellar domain. They are saurian creatures, possibly genetically similar to the Earth species of dinosaur, the Triceratops. Tough and aggressive, they are entirely herbivorous (plant eating), and have a high sense of loyalty to their race. Part of the reason for the Triceratons’ aggressiveness stems from a cosmological phenomenon occurring in the heart of their region of space. There is a region of destructiveness that is gradually spreading out from the hub of our galactic spiral. The exact cause of this stellar disaster is not known. The Triceratons deny any problem and laugh off the idea of a killer Black Hole. However, many stars in the region have gone nova, and there are accounts of refugees arriving at the outer Triceraton worlds. The best evidence of the galactic holocaust are the Triceratons’ asteroid homeworlds. Hugh asteroids are outfitted with gigantic ion drives and become mobile cities and military staging grounds for the expanding Triceraton empire. Special asteroids are dedicated to factories, universities, research centers, and even arens for sporting and gladitorial events. The Triceraton Republic is now engaged in an ongoing conflict with the Human Federation ("Federat"). A border region consisting of thousands of square light years has each side jockeying for position. Currently, the open warfare has subsided, as both sides continue searching for a weakness or a weapon to solve the impasse. There are many reasons for the success of the Triceratons. First is their eagerness to adopt new technology, and their willingness to change their tactics accordingly. A specific technological strengths that the Triceratons have exploited thoroughly is their atmospheric adaptability that allows them to self-mutagenically breathe otherwise unsuitable air. Some Triceraton agents take Xemorene, a highly addictive stimulative drug that increases speed and efficiency of the nervous system, the withdrawal effects leading to heart failure and death. In the aftermath of the Turtles’ accidental transportation to Triceraton space (during which time the Turtles competed in a combat tournament against four Triceratons in a "Tri-Sports" bout, then took the Triceratons’ Prime Leader hostage) upon their breaking into the TCRI building, three were accidentally transported along with the Turtles back to Earth (TMNT Vol. 1, #6 & 7). While one of them was captured by DARPA (TMNT Vol. 2, #9 - 13), and another, Zog, went into hiding in the sewers until Raphael discovered him prior to the Turtles’ second confrontation with The Shredder (TMNT Vol. 1, #19 & 20), the third transported Triceraton remains unaccounted for. After their accidental sojourn into Triceraton space and D'Hoonib, the Turtles were invited back to the TCRI homeworld, where they were reunited with the Fugitoid. Almost immediately after they arrived, Gavat-4 Station, an outpost that had a Transmat link directly to the Utrom homeworld, fell under heavy Triceraton attack. The Turtles agreed to help them, transporting themselves to the station and self-destructing it (TMNT: Guide to the Universe, Shell Shock). When the Turtles pursued DARPA in search of their brother, Raphael, missing after a conflict with a then-cyborg Dr. Baxter Stockman, they soon found themselves facing a Triceraton invasion in Nevada. The cityship that made up the invasion force (it followed the Turtles’ transportation signal from when they were accidentally transported there), falling apart from its long space voyage from Triceraton space, attempted to ram and decimate the Earth by slingshooting around the sun and engaging full Impulse Speed. This attempt, however, was presumably stopped by Louis Braunze’s extraterrestrial-captured "inter-phasic cannon," which he planned to use to move the Triceraton cityship out of phase, causing it to then harmlessly pass through Earth’s outer crust and re-solidify in the molten core, vaporizing the gigantic vessel (TMNT Vol. 2, #13).
Some TMNT stuff was always meant for grownups.
During his three year stay in the sewers in the Image Comics adaption of Teenage Mutant Ninja Turtles, the Triceraton Zog had evidently begun construction of a Triceraton aircar that Donatello would later discover and complete, then remodel (TMNT Vol. 3, #2 & 10). Eight Triceratons Transmatted to Earth when Leatherhead and his Utrom friend Dr. X tested their second attempt to build a working Transmat Device to get him "home" to the Utrom homeworld on Leonardo. The Triceratons had been looking for the Turtles for some time, and seized the opportunity to send a commando led by Captain Zak. Leonardo nearly killed one of the eight Triceratons with their own firearms, though Leonardo, Michaelangelo, Leatherhead, and Dr. X had to escape from harm's way. Lured by the homing beacon sent from the Turtles' aircar, Captain Zak has one of his Triceraton commandos translocate to the signal, appearing directly on top of the aircar as Donatello unsuspectingly pilots it home with Horridus/Sara. The Turtles managed to fight the Triceraton invasion to its climax, with the invaluable help and savage force of Leatherhead, who, along with the last Triceraton standing, was transmatted away to parts unknown (TMNT Vol. 3, #19 - 21).
Each Triceraton had different coloring and horn shapes.
The Triceraton Republic is a brutal society ruled by the despotic Prime Leader Zanramon. They wage war against the Federation, their sworn enemies. The Triceratons also have a serious combat thirst, like the Romans of Earth, and thus pit alien creatures against each other in coliseums. Despite its bloody appearance, the Triceraton Empire was once a grand republic and valued honor, until Zanramon took over. Soon, greed and corruption took over, turning the republic into a war-thirsty regime. The Republic appearently has a legislature that, after Zanramon's deposition, was reconfigured into a more republican legislature (as decreed by Traximus in Worlds Collide, Part 3).
The Empire's reign was upset during an attempt to capture Professor Honeycutt, a robot scientist who had befriended the Ninja Turtles. Hoping to steal the Professor's teleporter device, the Triceratons became embroiled in fresh battle with the Federation. During this time, they captured the Turtles and sent them first to prison, then to the gladitorial matches.
It was in these barbaric surroundings that the Turtles met Traximus, a noble warrior of the Triceraton Empire. He had been thrown into the games when Zanramon took over, and sought to break free. With help from the Turtles, who stole Zanramon's cruiser and then escaped back to Earth, Traximus and co. escaped. Traximus next appeared in the Battle Nexus, competing and looking for allies. He helped the Turtles in a fight against the evil Drako. Curiously, Traximus did not require a breathing mask in the Battle Nexus, for reasons which remain unknown.
The Triceratons trailed Honeycutt to Earth, where they invaded and did battle with the Turtles. They captured Donatello to extract the information. But Donatello didn't know where Honeycutt was. However, once it was determined that the professor had left Earth, the aliens departed. Unfortunately, Honeycutt just then returned, sparking another conflict between the arriving Federation and the returning Triceratons. However, Honeycutt managed to end the battle by infecting both sides with a virus. Zanramon ordered the Federation ships destroyed but any ship coming would be affected too. Commander Mozar thought it was not honorable.
It was then that Traximus' rebellion attacked. Dethroning Zanramon with the support of Commander Mozar, Zanramon's second-in-command, Traximus destroyed the leader's chair to symbolize the end of the empire and revealed that a Triceraton senate will replace the dictatorship. He then helped the Federation, and Zanramon and General Blanque, the former leader of the Federation forces, were both imprisoned to help ensure the peace.
In the Fast Forward season, a few Triceratons were seen as workers on Earth.
Triceraton technology is quite advanced, employing anti-gravity vehicles and energy blasters on a regular basis, on about the same level as the Federation. A notable trademark of Triceraton technology is the common triangular or pyramidical design on many vital systems, such as power cores and blasters.
The Republic was once a society of honor and glory, but with Zanramon takeover, the Republic lost the sense of their warrior's history. But thanks to Traximus, the old Republic was restored.
On one of the homeworlds, there is a place called "The Games", where helpless beings are pitted against each other for fun. But Triceraton gladiators is also available to the Federation, which is their number one show.