The kid who gave the Terminator orders
John hadn't been born yet in 1984: Kyle Reese, the soldier he himself sent back to protect Sarah, is his father. By 1995, 10-year-old John lives with foster parents, hacks ATMs with a laptop and thinks his mother, locked up at Pescadero, is crazy.
At a mall, the T-1000 tries to kill him and a T-800 saves him. John realizes the machine follows his orders. He tells it to break Sarah out and forbids it to kill. The T-1000 murders his foster parents, and John goes on the run with his mother and the T-800, teaching it slang and a bit of humanity. He convinces Miles Dyson to destroy his own research at Cyberdyne. At the steel mill, after the T-1000 is gone, he begs the T-800 to stay. The machine explains it has to be destroyed and says it now knows why people cry.