Miles Dyson was the genius behind translating the remains of a
T-800 found in a factory in 1984 into new
cybernetic innovations. He would eventually discover from the remains technologies that would one day birth
Skynet.
However, this eventuality was interfered with when travelers with knowledge of the future came into his life. First, a well-armed Sarah Connor decided the best way to avert the birth of Skynet and subsequent
fall of humanity would be to
assassinate the man responsible for the computer
conqueror.
Connor attacks the brilliant Dyson while he's working in his study, his family home with him. After many spent bullets and broken glass/equipment, Connor cannot bring herself to be a
Terminator herself, executing a man who's work itself was innocent and without malicious intent. She is still sobbing when her son, the young
John Connor, and his T-800
bodyguard arrive.
John, Sarah and the Terminator describe the events of the future to Dyson, and he comes to realize that he cannot continue working, for the sake of his family and humanity. On top of this, he tells Connor and company that the bulk of his work, including two artifacts from an earlier T-800 that fueled it all, exist at his place of work:
Cyberdyne Systems. Hearing this, they decide to go together and destroy all of the work for the sake of mankind.
Via some
sneaking and
hacking*, they manage to obtain the artifacts, and set up massive amounts of explosives to blow up the records and backups of all the data. However, by this time ploice have assembled and are trying to foil the would-be saviors of men. Dyson gets shot by police, and decides to stay behind as the others escape with the T-800 pieces to be destroyed/hidden. Dyson then takes position with the trigger in his hand, quickly dying. He positions himself to become a literal
Dead-Man's switch with a weight in his hand above the explosive's trigger, which will fall on it when he dies, which prevents the police from intervening (for if they try to remove him, he activates it earlier, and if they shoot him some more, he dies all the quicker. Either way,
Boom.)
The police opt the self-preservation route, and leave before Dyson perishes. A noble self-sacrifice, even if the Officers of the Law didn't understand the full scope of his actions.
----
The actor playing Dyson in
Terminator 2: Judgment Day was
Joe Morton.
Originally, Dyson's death scene was intended to be longer and more poetic, with a slight
montage sequence about his family, showing why he was sacrificing himself, but it was cut for time restraints and redundancy, seeing as most people can figure that sacrificing oneself for the good of your race is a good thing to do**.
* Room/premises hacking, that is.
** An opinion, of course. It may or may not be held by me ;)