Bio-Sentinels / Sentinelnaughts
Though the very concept of Sentinels was first imagined by Bolivar Trask, at least one model of Sentinels conceived by a Japanese national named Kaga 
owed none of its design from those that had followed in Trask’s footsteps. Like his fellow designers of Sentinels, Kaga hated the X-Men, though for different reasons. While others hated the X-Men for being mutants, Kaga hated them because they were beautiful. A mutant himself, Kaga’s mutations had made him hideous since birth, the result of his mother having survived the atomic bomb that had destroyed Hiroshima. Luckily for him, Kaga’s mutation also granted him enhanced intelligence and by the age of sixteen he was patenting technologies through front companies, earning him enough wealth to fund medical processes necessary to keep his failing body alive.
At first, Kaga was overjoyed when the X-Men debuted, but quickly soured when he saw that they seemed to fight mutants uglier than themselves. A master geneticist, Kaga began acquiring DNA from both living mutants and mutant corpses, providing him genetic material for eventually creating an army. One acquired mutant was the former Hellion called Paradigm, who had been transformed by the Phalanx virus into a techo-organic life-form. With Paradigm, Kaga managed to hack into the computer files of the Beast, who post M-Day had been researching the harvesting of X-genes from dead mutants to repopulate the species. Together with DNA acquired from the Brood, Kaga created Bio-Sentinels from the corpses of fallen mutants, transforming them into reanimated, super-powered automatons.
The first unit sent against the X-Men was deeply personal to the team, as it was constructed from the reanimated corpse of a fallen student, Wallflower. The second Bio-Sentinel, apparently created from some of the remains of the living island Krakoa, was actually not sent to attack the X-Men but to retrieve the first, to prevent the X-Men from examining it. After defeating it, the X-Men realized that some craft would have to retrieve both fallen units and secreted themselves on the cloaked ship when it appeared. The craft unknowingly brought the X-Men to Kaga’s facility, hidden in the mountains of northern Japan, where they confronted the mad scientist. Rather than exact revenge, however, the X-Men doomed the hate-filled Kaga to a worse fate, explaining that they ensure that he would receive the best possible medical care until he died of natural causes. Before departing, the X-Men activated the facility’s self-destruct, ending the threat of Kaga’s Bio-Sentinels. [Astonishing X-Men (3rd series) #31-35]
While Kaga’s Bio-Sentinels sought to construct Sentinels out of the biological, someone else sought to merge Sentinels with the biological. Actually, the man who would go by the name “Father,” wanted to merge all of mankind with the technological in an event futurists have long named “the Singularity.” In the early days of the Cold War and funded by the Weapon Plus program, Father and his two partners, who went by the aliases “Mother” and “Brother,” were tasked with creating an army of powerful androids, similar to the original, android Human Torch, which had proved so useful during the war. However, true life was never instilled into their creations until they utilized the Orb of Necromancy, which Brother had obtained from Merlyn of Otherworld. The resulting twenty “Descendants,” the first Homo-Synthezoidus,” were to be the final stage of life on Earth.
Bickering between the three creators stymied further success. Brother refused to create a new species with which humanity would need to compete and he disappeared with the Orb of Necromancy. Meanwhile, Mother released the Descendants into the world. As the decades passed and the Descendants intermingled with humanity, Father continued his work, acquiring technological beings wherever he found them and reprogramming them to his cause. Among the many models enlisted to his cause were several Sentinels, including at least two Master Molds. In a secret underground base called the Core, these self-named “Sentinelnaughts” waited with the rest of Father’s robotic army, comprised of Doombots, Adaptoids, Reavers, Deathloks, Machine People and Ultravisions, for the day when one of the Descendants would naturally reproduce with an ordinary human, thus proving that the Singularity, or as Father called it “the Event” was possible.
Eventually, Father was proven right when his adaptoids learned of a young Descendant-born Pakistani boy named Pervez, and ordered his synthezoids to retrieve the boy and his mother. Unfortunately for him, Father’s plans were complicated by the intervention of the covert, “Secret” Avengers team, which followed the robots to the Core to rescue the boy. By coincidence, among the Avengers was the original Human Torch, whom the citizens of the Core revered as “Grandfather.” When the Avengers closed in on Father, a Master Mold unit pleaded with him to join their cause. Undeterred, the Torch fought the Sentinelnaught and destroyed it by activating its self-destruct, which covered the Avengers’ escape. [Secret Avengers (1st series) #22-25]
Seemingly thwarted, Father had only suffered a minor defeat and proceeded with his plans for the Event, which included releasing a mist of nano-tech designed to transform all of humanity into Descendants. The largest and most powerful of Father’s robot army, a second Master Mold was tasked with singlehandedly sealing the Avengers and Fantastic Four within their respective towers to prevent their interference. Already outside during the attack, even Captain Britain and a towering Giant-Man seemed no match for the Master Mold unit, and with the spreading of the techno-mist all seemed lost. At the last minute, however, the original Human Torch destroyed the Orb of Necromancy, in the process deactivating all of Father’s robots, including the Master Mold. After watching the light sputter and dim from the massive Sentinel, Captain Britain placed it in orbit, possibly allowing it to be destroyed later in an uncontrolled reentry. [Secret Avengers (1st series) #34-37]
Sentinel Arms Race
In the years since the first Mark I model of Sentinels had been debuted by Bolivar Trask, most of the governments of the world had possessed, or still operated, their own variation of Sentinel program as part of their national defense. In the wake of the mutant Decimation following M-Day and the X-Men’s status as leaders of most of the world’s remaining mutant population at the independent island nation of Utopia, X-Men leader Cyclops decided to do something about it. Accompanied by Wolverine, Cyclops addressed an international arms control conference in Switzerland, requesting that the world’s governments decommission their programs and offering the X-Men’s help in demolishing the units already existing. What Cyclops could not know was that, in doing so, he had walked into the plans of a young man named Kade Kilgore.
Though a baseline human, Kade Kilgore possessed incredible intelligence, which was rivaled only by his ambition and his antipathy toward the rest of humanity. At the age of twelve, Kade had been planning the overthrow of his father for two years, having no patience to wait in order to inherit the world his father promised would be his. Kade struck a deal with the Inner Circle of the Hellfire Club, which had recently once again become controlled entirely by humans. In exchange for killing his father for the Club, all of whose members detested him, Kade would be made their new Black King. To sweeten the deal, Kade would orchestrate a new arms race of Sentinel production, which they would all profit in manufacturing. [Wolverine and the X-Men (1st series) #16, X-Men Schism #1]
Along with three other prodigies his own age, Kade used advanced technology at his disposal to free anarchist former-Xavier Institute student Quentin Quire on the eve of the Swiss arms control summit. As Kade predicted, Quentin caused a horrific scene at the conference, panicking the world’s governments, many of which quickly reactivated their existing Sentinels. However, as Kade had also predicted, these were long obsolete Mark I & Mark II models, which badly malfunctioned and even turned on the countries which possessed them. Immediately, the X-Men rushed to assist, once again literally saving the world that hated and feared them by destroying the malfunctioning Sentinels activated as deterrent against them. However, this too was part of young Kade’s plan, as it left Utopia bereft of its most powerful defenders. When the few X-Men who remained attended the opening of a mutant history museum, Kade and his forces struck, surprising and even overpowering the attending X-Men. [X-Men Schism #1-3]
With Utopia now completely undefended, save for the young and untrained students, Kade enacted his true plan, the demonstration of a new weapon. Seemingly a simple suitcase bomb, the resulting debris from the bomb’s explosion began to coalesce into a new, gigantic Sentinel. Drawing and absorbing anything along its path, the Sentinel made a direct line to Utopia, becoming larger and more powerful as it got ever closer. Ultimately, the island’s defenders stopped and destroyed the Sentinel, though at a high cost. The argument between Cyclops and Wolverine, the only experienced X-Men left on the island at the time, over whether the island’s children should fight or flee caused a schism between the X-Men, splitting Utopia’s citizens into two camps.
None of this mattered to Kade Kilgore, who didn’t even care that his Sentinel failed. The entire affair had demonstrated to the world’s governments how weak and outdated their bulky old Sentinels models were and the attack on Utopia had shown them that Kade Kilgore possessed technology which could build a Sentinel out of something the size of a suitcase. With orders now pouring in by the thousands, Kade was set to profit in billions. Better still, with the Hellfire Club having served their own purpose, Kade arranged the murder of its members and installed his three young co-conspirators as their replacement queen and bishops.[X-Men Schism #3-5]
In short order, on a private island somewhere in the Indian Ocean, Kade began showing prospective buyers his newest models. The Mark X model was the “suitcase Sentinel” he had already publicly demonstrated. The Mark XI was a transformable, all-terrain model for “murder by land, air or sea.” The Mark XII were nanobot Sentinels, sold in bundles of five-thousand and operated like swarms of killer bees but made of metal and armed with lasers. The Mark XIII was modeled after the magically-created Tri-Sentinel, though this unit was powered by its own miniaturized nuclear reactor.
While demonstrating these models to government representatives from across the globe, the facility was attacked by the Phoenix Five, Cyclops and four members of his X-Men who had recently been imbued with the sum power of the Phoenix Force. Though the five cosmically-powered mutants destroyed the whole facility, Kade Kilgore merely saw the whole exercise as another form of advertisement to his prospective customers around the world, who through the five’s actions had yet another reason to fear mutants. [Wolverine and the X-Men (1st series) #16]
In the Sentinel arms race, not all saw them as weapons against mutants. Some saw them as weapons of war against their fellow nation states. Small in size and landlocked by historical enemies, the economically and militarily weak land of 
Puternicstan had been passed back and forth between the more powerful nations of Latveria and Symkaria over the preceding two centuries. Wishing to take a step toward true independence, the state’s leader, Governor Strelonivich, had been acquiring Sentinels for some time from the black market. Unfortunately for her, however, most of the units acquired were defective in one manner or another.
Fortunes shifted for the governor when Puternicstani special forces intercepted the sale of three units between Georgian and Chechen groups. From the three units, Puternicstani engineers were able to cobble together two fully functioning units. From these two, the military found that they were able to control remotely the dozens of barely functional units, creating an instant Sentinel army. Against the recommendation of her head of military, General Nobakov, the governor launched them all against neighboring Symkaria.
As it happened, however, Puternicstan’s acquisition of the three Sentinels had been witnessed by the X-Men’s Security-Recon operative Domino, who reported it back to the X-Men. A small X-Men security squad, led by Storm, arrived in Puternicstan just as the Sentinels went online. Aided by War Machine, who had been sent by the US government and NATO to help prevent the situation’s escalation, the X-Men managed to prevent the Sentinel army from invading Symkaria and deactivated their control mechanism. In the aftermath, Governor Strelonivich was arrested and the nation left under the leadership of General Nobakov. Presumably, what remained of the Sentinel army was destroyed. [X-Men (3rd series) #20-24]