Sinistron was designed and created by Will Magnus to be the ultimate sentinel. The hatred that Will Magnus had for his brother, Magneto, was encoded into Sinistron's synthetic mind along with the seeds on sentience that allowed Sinistron to overcome his programming and rebel against his master. Seeing the potential mutants had for destruction, Sinistron began to capture mutants and bring them back to his citadel on Genosha where he would control their minds to turn them into an army to conquer the world.
This got the attention of Magneto and his Magnetic Men. Sinistron escaped their first battle, but was tracked back to Genosha were he was ready to face his pursuers again. Magneto tried to disable Sinistron's electronic mind with an electromagnetic attack, but had his own mind frozen when Sinistron reversed the attack on him. This allowed the Magnetic Men to break free of Magneto's control, which froze them when his mind was frozen, and attack Sinistron and break his hold on Magneto. Magneto continues his assault and destroys Sinistron's body, but he escapes again this time in a miniature drone that contained his consciousness.