Short answers, pulled from the story.
The Linn LM-1 Drum Computer, released in 1980 at a price of $4,995, was the first commercially released drum machine to use digital samples. Only about 500 units were ever made, but it can be heard on hundreds of hit records from the 1980s. Prince bought one of the first LM-1s and used it on albums including 1999 and Purple Rain.
Roland discontinued the TR-808 after building approximately 12,000 units because its required semiconductors became impossible to restock. Cheap used units then reached underground musicians who prized its analog bass drum sound. It eventually appeared on more hit records than any other drum machine and became a cornerstone of hip hop, electronic, and dance music.
"Saved by the Bell" by Robin Gibb was the first major pop song to use a drum machine. It reached number 2 in Britain in 1969. Sly and the Family Stone's "Family Affair" later made them the first group to reach number 1 on the pop charts with a drum machine-driven record.
The earliest purpose-built rhythm machine, the Rhythmicon, was developed by Léon Theremin in 1930-32 at the request of composer Henry Cowell. Harry Chamberlin built the Chamberlin Rhythmate in 1957, and Wurlitzer released the Side Man in 1959. The first fully transistorized, commercially sold rhythm machines came in 1964 from Seeburg.
The TR-909, introduced by Roland in 1983, was the first Roland drum machine to use MIDI and the first to use digital samples for some sounds. Like the 808, it was a commercial failure but circulated cheaply on the used market. Alongside the Roland TB-303, it shaped the development of techno, house, and acid music.
Korg originated as Keio-Giken, founded in Tokyo in the early 1960s when nightclub owner Tsutomu Katoh backed accordion player Tadashi Osanai in building a better rhythm machine than the Wurlitzer Side Man. Their first product, the Donca-Matic DA-20, was released in 1963 and cost roughly the equivalent of an average annual Japanese income at the time.