When it first appeared on the market in the early 1980s the Roland TR-808 could be purchased at about a quarter the price of competing brands. Imitation drums sounded cheap, too.
These were not digital samples, but simple analog circuits. The bass drum sound was a strange, deep, ringing thud; the snare was a high, papery snap; the cowbell was an obnoxious clank.
But, maybe because it was so unlike real drums, the 808 was the perfect sound for 1980s pop. Its very artificiality made it sound new, and its low cost and convenience was perfect for the production budgets of early underground hip-hop records. I would say that rap probably wouldn't have existed as we know it without the 808.
I associate the Roland TR-808 drum machine most with old skool rap records; here’s an example from the Beastie Boys’ classic “Brass Monkey.”