Short answers, pulled from the story.
John Ambrose Fleming patented the first vacuum tube, known as the Fleming valve, in 1904. This device was a glass envelope evacuated of air containing a heated filament and a metal plate that rectified radio signals for the Marconi Company.
Lee de Forest invented the first electronic amplifier vacuum tube, the Audion, in 1906. He inserted a third electrode, a wire grid, between the filament and the plate to control electron flow and amplify signals by hundreds of times.
Harold D. Arnold developed the hard vacuum triode for AT&T in 1912. He realized that residual gas caused instability and created high-vacuum triodes that enabled the first coast-to-coast telephone line in the United States by 1915.
The Colossus computer designed by Tommy Flowers used over 1,600 vacuum tubes to break German Lorenz encryption during World War II. Successor models of the machine utilized about 2,400 tubes to process data at speeds electromechanical devices could not match.
The largest commercial vacuum tube, the Eimac 8974, can dissipate 2.5 megawatts of heat. This power level dwarfs the largest power transistors available today and required water-cooled anodes to manage the thermal load.
The transistor began replacing vacuum tubes in the 1960s. Despite this transition, the 12AX7 dual triode remained the standard for guitar amplifiers and the cathode-ray tube stayed the standard for television receivers and computer monitors until the early 21st century.