Sinister

Nathaniel Essex, a brilliant scientist and geneticist, was one of the first men in the world to discover the mutant gene. He made it his life's work to create the perfect mutant. Because of this work and his own amazing mutant abilities, Sinister was the first mutant Apocalypse brought into his fold, becoming the first and best Horseman. Sinister was at Apocalypse's side when they witnessed the death of Charles Xavier, the same day Apocalypse declared war on humankind. In the early days of this partnership, Sinister adopted the Summers brothers who both had exceptional mutant abilities. Alex and Scott were the closest Sinister had come to finding agenetic perfection. Scott's genes were of particular interest to Sinister; he hoped to one day use them to create the world's powerful mutant.

Sinister would create, alongside the Dark Beast, the process used to create Apocalypse's Infinite army. The two controlled the Pens, a mutant breeding and testing ground for their twisted genetic plans. Sinister was crucial in enhancing members of Apocalypse's army and in carrying out his directive of survival of the fittest. He eventually discovered that the combined DNA of the captured X-Man Jean Grey and his adopted son, Scott Summers, would create a mutant stronger than any other, even Apocalypse. Sinister carried out his creation and hid the experiment, named Nate Grey, with a small traveling theatre troupe of mutants.

As time moved on and Apocalypse's rule became more fanatical, Sinister realized his vision of the future did not coincide with his master's. Betraying Apocalypse, he revealed his master's plan to unleash a sneak attack on the humans in Europe to Weapon X and Jean Grey. This led to the Human High Council preparing a full-scale nuclear assault on Apocalypse's kingdom in America. Sinister blew up his hideout and all the secrets it held inside. He traveled the ruined countryside of America, searching for Nate Grey. Sinister infiltrated his group under the name Essex and became close with his creation. His identity was discovered by Nate's friend, Brute, who recognized Sinister from the breeding pens. Sinister murdered Brute and Nate's mentor, Forge, in cold blood. Nate found his murdered friends and, enraged, unleashed his full mutant powers on Sinister. As Nate walked away, Sinister fell to the ground and apparently died from massive internal injuries.