Miles Dyson is the scientist whose work leads to Skynet in Terminator 2: Judgment Day. He is the Cyberdyne Systems engineer developing the technology that will eventually produce the artificial intelligence responsible for the machine war.
Sarah Connor initially views Dyson as a direct threat after learning that his research is connected to Judgment Day. She travels to his home intending to kill him, but John and the reprogrammed T-800 intervene. They instead explain the future consequences of his work and take him to Cyberdyne Systems.
Dyson ultimately helps destroy the research and the Terminator arm and processor that could advance it. He dies when the Cyberdyne building is destroyed, making his decision a crucial part of the film’s attempt to change history.
Miles Dyson is not the same person as Danny Dyson, his son, who appears in Terminator: Dark Fate. The two characters belong to different stages and continuities of the franchise.