Hal Finney had a major impact in cryptography. He played a crucial role in the development of PGP email encryption and became PGP's first employee. Similarly, he was one of the first developers of Bitcoin protocol; he download the Bitcoin software the day it was released and was the recipient of the very first Bitcoin transaction (10 BTC from Satoshi Nakamoto --> Hal Finney). Many have speculated that Finney was the pseudonymous Satoshi Nakamoto:
[H]e quickly saw the promise of the Bitcoin project when it was announced on an obscure email list in 2008 by a creator with the pseudonym Satoshi Nakamoto.
Bitcoin used some of the same cryptographic tools harnessed by P.G.P. and held out the promise that participants could choose to be anonymous when spending money online.
When the project drew criticism from other cryptographers, Mr. Finney was among the first people to defend it. He downloaded the Bitcoin software the day it was released. The day after that, he took part in the first transaction on the network when Satoshi Nakamoto sent him 10 Bitcoins.
His early work on Bitcoin and his programming background led to frequent speculation in the Bitcoin community that Mr. Finney was Satoshi Nakamoto, a claim he always denied.