Bitcoin did not come from nowhere. It combined ideas that cryptographers had worked on since the early 1980s.
DigiCash (1982–1990s)
David Chaum's paper Blind signatures for untraceable payments (Crypto '82) showed how a bank could sign digital coins without seeing who spent them. His company DigiCash built it, but it still needed a central bank-like issuer – and when the company failed, the money went with it.
Hashcash (1997)
Adam Back proposed making each email cost a little computing work to fight spam. That idea – costly, easily verified proof of work – became Bitcoin's mining engine.
b-money (1998)
Wei Dai described money created by solving computational problems and tracked by a network of pseudonymous participants, inspired by the cypherpunk vision of a community where "violence is impossible".
Bit Gold (2005)
Nick Szabo described chaining proof-of-work results to create scarce, unforgeable digital "gold".
RPOW (2004)
Hal Finney built reusable proofs of work. In his own words, this is why he "found Bitcoin fascinating".
The missing piece
Each design either needed a trusted server or left open how strangers agree on who owns what – the double spending problem. Satoshi's whitepaper cites b-money and Hashcash and solved the gap: the longest proof-of-work chain is the shared record, with no one in charge.