Roland TB-303
1981-1984
The TB-303 was an analog synthesizer intended to be a bass accompaniment for solo guitarists. It flopped because it sounded nothing like a bass guitar. And it was notoriously difficult to use - the manual weighed more than the machine. Absolutely no one wanted it.
The synthesizer was rediscovered almost ten years later and it became essential to the emerging Acid House music style. Roland made this new retro version, since apparently now everyone wants one.
Additional info:
Djtechtools.com - History Of The TB-303: Roland’s Accidental Legend