John Bardeen
The first working transistor was a point-contact transistor invented by John Bardeen and Walter Houser Brattain at the Bell Telephone Laboratories (BTL) in 1947. William Shockley then invented the bipolar junction transistor at BTL in 1948. While early junction transistors were relatively bulky devices that were difficult to manufacture on a mass-production basis, they opened the door for more compact devices.