They are mirror images of each other; Tomax's hair is parted on the right side of his head and Xamot's on the left, the piping on their uniforms goes up the opposite side on each twin, and even their names are mirror images of one another—with Xamot reading as Tomax in a mirror. The only distinguishing mark between the two is a scar on Xamot's right cheek, which Tomax does not have. Tomax and Xamot share an empathic connection commonly known as "The Corsican Syndrome" in which identical twins are believed to be psychically bonded, as per The Corsican Brothers. While this is often useful, as it allows them to communicate wordlessly and finish each others sentences, it is also a liability as they feel each other's pain.
While their origins are top secret, the brothers speak in notable accents that indicate they were born on an island in the Mediterranean (While never actually named, this island is strongly implied to be Corsica). The brothers served in the French Foreign Legion in Algeria, then as mercenaries in Africa and South America before changing careers and moving into banking, becoming bankers in Zurich, Switzerland. Unhappy with the world of corporate finance, the brothers found the opportunities available in international terrorism far more suited to their abilities and joined Cobra. Within Cobra, their specialties are in infiltration, espionage, sabotage, propaganda and corporate law.
Like the Crimson Guard that they lead, Xamot and Tomax also lead the "respectable" corporate face of Cobra as the founders, owners, and CEOs of Extensive Enterprises. When not engaged in terrorism, they efficiently manage Cobra's business affairs in shirt and tie. Their preferred mode of attack is through brains over brawn, using the law to serve the purposes of Cobra. They have covered their paper trail and connection to Cobra so well that it is thought to be impossible to prove a connection between them and the terrorist organization.
In one of their earlier appearances, they confront G.I.Joe forces throughout a busy amusement park.
Their forces, the Crimson Guard, are shown as capable battlefield soldiers and respectable businessmen. As the latter, they are to gain as much economic influence as possible, solely for the benefit of Cobra.
In issue #56, a Joe team, assisted by Sierra Gordo revolutionaries, captures a Cobra fortress Terrordrome. The twins, having prepared, purposely wait until the Joes are inside before attempting to activate several explosive devices. This fails, as the Joes had brought their own explosive expert, Tripwire.
In issue #109, the Twins and their forces do capture a squad of Joe members. They misinterpet an order from Cobra Commander and incorrectly believe that they must now execute all the Joes. Unwilling to outright kill the subdued prisoners, they back off. A willing S.A.W. Viper fire into the prisoners, killing many. The survivors injure the Viper with a hidden knife and escape. In the ensuring pursuit, the prisoners commandeer a Cobra vehicle, which is fired upon by other Cobra forces. Even more Joes die; the resulting survivors from that incident make it back to Joe territory.
Years later, in the Devil's Due series, the Twins are shown once again as loyal employees of Cobra Commander. They perform a personal mission for him and even reactivate long-dormant sleeper agents to provide needed personnel.
They continue to broker most deals for Cobra, and were in charge of the secret construction of Monolith Base in Badhikstan, but after G.I. Joe raided the base, they fled with Cobra Commander to a cave. There, Red Shadow agent Dela Eden arrived and unleashed gunfire on the group. They later turned up alive, working with the Commander in a smaller, scaled down version of Cobra.
In the recent G.I. Joe Special Missions: Antarctica one-shot, a Joe team broke up an illegal oil drilling operation that was run by Tomax, who was able to escape. During the story, Xamot was strangely absent. In one scene Tomax talked to his brother as if he were present, despite the scene showing an empty chair. The whereabouts of Xamot were revealed in a backup story in the same issue, when G.I. Joe raided a Cobra medical facility and found Xamot, in a coma and unresponsive (presumably from the Red Shadows attack). Xamot is currently in G.I. Joe custody, still in a coma.
In America's Elite #30, Tomax leads a raid on "The Coffin", a G.I.Joe maximum-security prison located in Greenland, to rescue his brother and free other Cobra operatives.
At the beginning of the second season, Tomax and Xamot join Dr. Mindbender and Destro in creating Serpentor, having tired of Cobra Commander's failures. But as soon as Serpentor is brought to life, and orders his attack and invasion of the United States, Tomax and Xamot are the first to point out the sheer impossibility of such an attack, their objections are quickly silenced however, when Serpentor begins to throttle them. In G.I Joe: The Movie, they side with Cobra-La and are seen fighting the Joes in the final battle until a huge explosion that destroys all of Cobra-La.
In the unproduced third season of the original Sunbow series, Tomax and Xamot were planned to be the season's main villains, with most of Cobra-La and the Cobra Organization being destroyed at the end of the movie. Tomax and Xamot would then form a new criminal organization known as the Coil to fight against the Joes. This season never went into production due to the abrupt cancellation of the series by Hasbro.
Tomax and Xamot are not seen again in the DIC-produced third season. Although their old headquarters, the Extensive Enterprises building, is seen, and General Hawk mentions that they closed them down. The building itself has been abandoned and is being used as a secret Cobra base. Also in the DIC third and fourth seasons, their troops, the Crimson Guard are shown in the form of the Crimson Guard Immortals. However, they are used more as a grunt force as opposed to an elite group.