In December 1947, John Bardeen and Walter Brattain at Bell Labs demonstrated the first working transistor, with William Shockley soon developing the more practical junction transistor. The three shared the 1956 Nobel Prize in Physics.
Why it mattered
A transistor is a switch and amplifier with no moving parts, no heat-up time and a tiny footprint. It replaced the fragile, power-hungry vacuum tube, and — crucially — it could be made smaller and smaller. Every chip in every device you own is, at bottom, billions of transistors. Nothing else on this timeline happens without it.