William Shockley, John Bardeen & Walter Brattain, co-invented the transistor
Transistor inventors Shockley (seated), Bardeen and Brattain, 1948. (Courtesy AT&T)
One of the most famous and influential inventions to come out of the Bell Labs was the transistor. As the first solid state amplifier or switch, the transistor replaced the vacuum tube--perhaps making science fiction movies less visually interesting, but paving the way for some real science, as the transistor helped lay the foundation for modern electronics.
Shockley, Bardeen and Brattain initially were studying the properties of germanium crystals and whether they could be used as semiconductors, as part of an attempt to replace troublesome, high-maintenance vacuum tubes as mechanical relays in telecommunications. The research led to the invention of the "point-contact" transistor, which, when electrical current was applied to one gold-foil contact, amplified the current via the germanium thereby boosting the strength of the current flowing through the second contact.
The team quickly improved on this device, developing the junction transistor, which was first used commercially in 1952 with the Sonotone hearing aid. The first transistor radio was manufactured in 1954. In 1956, the team received the Nobel Prize in Physics for their invention.