Short answers, pulled from the story.
Banū Mūsā, a Persian engineer from the 9th century, created the first known programmable music sequencer. This device was an automatic flute-playing machine powered by steam that used exchangeable cylinders with pins to control air flow.
Roland released the MSQ-700 as the first MIDI sequencer when it hit the market in 1983. General-purpose computers began playing a role as sequencers only after this advent of the standard.
Max Mathews created MUSIC, the first widely used program for sound generation, at Bell Labs in 1957. A seventeen-second composition performed by an IBM 704 computer brought his work to life shortly thereafter.
Electronic Music Studios released one of the first digital sequencer products in 1971 as part of the Synthi 100 module. Oberheim followed with the DS-2 Digital Sequencer in 1974 and Sequential Circuits introduced Model 800 in 1977.
Roland founder Ikutaro Kakehashi proposed standardization between different manufacturers instruments in June 1981. He discussed the concept with Tom Oberheim from Oberheim Electronics and Dave Smith from Sequential Circits before unveiling the MIDI standard in 1983.