In the Terminator movies, Skynet is trying to kill Sarah and John Connor, sending various terminators from the future to hunt them down.
So my question is: who made the time machine to go back to past? Did Skynet do so, or was it previously made by humans and then taken over by Skynet?
According to the official novelisations of the first and second films, the Time Displacement Equipment (TDE) was developed by Skynet.
As far as Reese knew, he was the first living man to be temporally displaced. Skynet had developed the hardware as part of its voracious research and development, a geometrically expanding computer-generated repertoire of new technologies.
The human raiders had seized the place intact, and the techs had scurried to download the system files and analyze them. When they realized what Skynet had done in its coldly rational desperation, John had opted to use its own technology as counterforce. But when Reese had stepped into the biaxial node of the field generator, no one really knew if the time displacement was survivable. He might have arrived in 1984, an already-cooling bag of meat, his heart stopped by unfathomable energies.
Kyle Reese had taught her this paranoia, learned from years of scrabbling in the postwar ruins, fighting off killer cyborgs and renegade humans. He'd been a soldier most of his life, he had said. It was the only way to have a life, up there in the future. Upthen, he'd called it. Where huge war machines rolled over the bones of millions; the dead, the flash-burned or the irradiatedout-of-existence. But John Connor had rallied the pitiful survivors into a threadbare resistance force. And little by little, humanity began to take back territory from the metal masters. Until one day the tide of battle turned, and Skynet, in a desperate burst of brilliance, devised time displacement, the first tactical time weapon. It sent a lethal emissary back through time to find and eliminate Sarah, so that John Connor might never be born.
But John's forces took control of the time displacement device and sent Kyle through, to stop the Terminator, if possible. It was essentially a suicide mission, and yet he had volunteered for it. He was a simple soldier about to walk point into the gaping maw of history because he loved Sarah.
In the novelisation of the first film, it was noted that the reason Kyle materialised in mid-air when he arrived in 1984, rather than on the ground, was due to the Resistance's lack of familiarity with the TDE.
He rubbed his arm unconsciously—a bloody scrape where he came down. The techs had brought him in high. With so little time to familiarize themselves with the displacement-field equipment and its calibration, they must have erred on the side of safety. Better than materializing knee-deep in pavement. Right.
The Terminator novelisation by Randall Frakes