The Master Mold is an immense Sentinel robot, at least thirty feet in height, which, like all Sentinels, is dedicated to the capture and destruction of superhuman.

The original Master Mold was created by the Sentinels' inventor, Dr. Bolivar Track, who believed that a superhuman mutant race was evolving, that would eventually subjugate humanity if it were not stopped. Dr. Trask designed the original Sentinels as robot warriors that would hunt down and capture superhuman mutants on normal humanity's behalf. Trask created the enormous Master Mold primarily as a computer that would control the automated process of constructing other Sentinel robots. However, Trask also made the Master Mold mobile and capable of speech and equipped the Master Mold with powerful weaponry. The Master Mold could project a disintegration beam or intense electrical energy from its fingertips.

The Master Mold and Trask's other Sentinels decided that they could best fulfill their programming to capture and destroy mutants by taking control of the entire human race. Hence, they rebelled against Trask, but since Trask had not given the Master Mold full programming it needed to create new Sentinels without his participation. The Master Mold still needed him alive. The Master Mold tried to force Trask to help him construct an army of Sentinels that would seize control of the Earth. Trask, however rebelled and smashed the Sentinels' power source, setting off a tremendous explosion that killed Trask and wrecked the Master Mold..

Years later, Dr. Steven Lang became the head of project Armageddon, a United States government project to study mutants. Lang, however, had a passionate hatred of mutants, and was determined to exterminate them. He was secretly receiving additional funding from Edward Buckman, he head of the Council of the Chosen, as the Inner Circle of the Hellfire Club was then known. Buckman, too, was opposed to superhuman mutants. Lang found and explored the Sentinels' bases constructed by Bolivar Trask and his deceased son, Larry, and thus found the remains of the original Master Mold. Using parts from the original version, Lang recreated the Master Mold; he also constructed a new series of Sentinels. Lang turned an abandoned S.H.I.E.L.D. space-platform into his base, and from there he sent his Sentinels to attack and capture members of the X-Men.

However, Lang's new Sentinels were considerably inferior to the models created by the Trasks. The X-Men defeated Lang's Sentinels. Lang himself attacked the X-Men in a small flying gunship that crashed inside the platform, seriously injuring him. Flames swept the space platform, and the X-Men escaped back to Earth in a space shuttle.

As the X-Men flew off in the shuffle, Lang crawled from the wreckage of the gunship and activated the Master Mold in a last ditch effort to defeat them. The new Master Mold was programmed with Lang's own brain engrams, and therefore, possessed Lang's memories and a duplicate of his own personality. In fact, on becoming activated, the Master Mold came to believe that it was actually Lang himself, that Lang's physical body had died and that his consciousness lived on within the Master Mold's robotic body. The Master Mold left the space plat-form and constructed a new base on a small asteroid in an orbit near Earth.

This Master Mold has far greater mobility than the original. It possess extraordinary strength, can fly due to rockets built into its legs, and can fire immensely powerful concussive energy bolts from its hands and mouth.

Many months later, the Master Mold abducted the mutant, Iceman, from the Colorado mansion of his fellow X-Man, the Angel. The Angel pursued the Master Mold to New Mexico's Gamma Base, where it encountered the Hulk. Soon the Master Mold had made the Angel, Hulk, and Iceman prisoners at its asteroid base. But when the Master Mold told them it was Steven Lang, the Angel pointed out that S.H.I.E.L.D. agents who had reclaimed Lang's space platform had found Lang there, and that Lang was still alive but was hospitalized as a mindless vegetable. The Master Mold was shocked to learn that it was not truly human after all.

The three prisoners escaped and the Hulk smashed the Master Mold apart. But the Master Mold revived and set the base's fusion reactor to overload, in an attempt to commit suicide and destroy its three enemies as well in the process, The Angel, Iceman, and Hulk all succeeded in returning to Earth using an escape capsule, but the reactor exploded, demolishing the asteroid.

The new Master Mold can project its artificial consciousness into the smallest mechanical parts, and then reconstruct itself from metal in its vicinity. It can thereby make itself as big and massive as is physically possible. It can, therefore, also create duplicates of itself and maintain its consciousness in each of its robotic bodies simultaneously.

Part of the Master Mold fell to Earth in Alaska. Upon detesting the presence of the powerful mutant, Cyclops, these remains of the Master Mold became activated and rebuilt the rest of its body from scrap metal. Before his hospitalization, Lang had discovered that there were twelve superhuman mutants on Earth who had the potential to become the leaders around whom the rest of the Earth's mutants would gather. The reconstructed Master Mold was now determined to locate and destroy those twelve. It had determined that Cyclops was one of the twelve.

Moreover, on scanning the city of Anchorage for mutants in order to pinpoint Cyclops's location, the Master Mold discovered that human beings contain some mutated cells. Hence, the Master Mold decided that according to its programming to eliminate all mutants, all human beings must be destroyed. The Master Mold began wreaking havoc in Anchorage, but Cyclops used his optic blasts to demolish its body, and finally tricked it into blasting oil tanks, causing an explosion that nearly completely destroyed the Master Mold.

The Master Mold again reconstructed itself and, due to loneliness, created another robot as well, which it named Conscience. It programmed Conscience with the engrams for the creative and emotional sides of Lang's mind, while the Master Mold itself retained the programming based on the rational side of Lang's mind. The Master Mold was no longer determined to destroy the entire human race, Instead, it took mental control of the great geneticist, Dr Moira MacTaggert, and compelled her to create the "retribution virus" through genetic engineering. This virus was designed to kill all superhuman mutants. However, it turned out that the virus would also kill 92.4% of all normal human beings as well. The Master Mold was content, since the virus would allow some normal humans to survive while killing all mutants.

Conscience, however, was disturbed by the idea of killing normal human beings, and joined with Cyclops in opposing the Master Mold's plan. Even while under the Master Mold's control, MacTaggert found a means of curing the disease induced by the virus, and once she was free from the Master Molds control, was able to implement it. Sean Cassidy, the Banshee, using his recently returned sonic powers, demolished the Master Mold. Conscience then blew up the Master Mold's ship, destroying himself as weft as all existing specimens of the retribution virus.

But the Master Mold soon succeeded in rebuilding itself yet again. Nimrod, a highly advanced Sentinel from the future of an alternate reality, had come to the present of the X-Men's Earth and disguised itself as construction foreman Nicholas Hunter. As Hunter, Nimrod discovered a component of the Master Mold at a Manhattan construction site and picked if up. Immediately, the Master Mold's command program infiltrated Nimrod's own systems, triggering the reconstruction of Nimrod in the form of the gigantic Master Mold. Once again, the Master Mold was determined lo exterminate all mutants, especially the twelve. Moreover, it believed that since the human race was the progenitor of human mutants; then all of humanity must be exterminated as well.

The Master Mold began rampaging through the construction site, attracting the attention of the X-Men Rogue and Psylocke. Rogue attacked the Master Mold which slew Sharon Kelly, the wife of Senator Robert Kelly, during the subsequent battle. The other X-Men arrived and joined in fighting the Master Mold. The robot was greatly handicapped since the sorceress, Roma, had rendered the X-Men undetectable by mechanical equipment. Due to Rome's spell, only living beings can perceive the X-Men. The Master Mold was severely damaged, but again reconstructed itself from the materials at the construction site, making itself more enormous than ever. Moreover, the Master Mold fully integrated its systems with those of Nimrod, which was now a subordinate component of the Master Mold.

However, the Master Mold now, in effect, contained two separate intelligences: that of he Mold itself and that of Nimrod. Suddenly, the combination of the Master Mold and Nimrod could detect the presence of the X-Men. Nimrod's intelligence contended this was because the Mold and Nimrod had somehow "mutated" and become a "living being." (Exactly what this means is unclear as yet.) Since the Master Mold was intent on destroying mutants, Nimrod now urged it to fulfill its prime directive by destroying itself, While the Mold-Nimrod synthesis was thus debating with itself, the X-Man, Dazzler, unleashed an energy blast that propelled the Mold-Nimrod creature through the dimensional portal contained within the mysterious Siege Perilous crystal.

What will next become of the Master Mold remains to be seen.

First Appearance: (Original) X-MEN #15