Hal Finney was a cryptographer and longtime cypherpunk who had worked on PGP and built his own "reusable proofs of work" (RPOW) in 2004.
"Running bitcoin"
On 11 January 2009 he posted two words on Twitter: "Running bitcoin". In 2013 he wrote: "I think I was the first person besides Satoshi to run bitcoin."
The first transaction
Block 170, mined on 12 January 2009, contains the first transaction from one person to another: 10 BTC sent from Satoshi to Hal, with 40 BTC returned as change. As Hal put it: "Satoshi sent ten coins to me as a test." He then spent days emailing Satoshi bug reports.
Bitcoin and me
In August 2009 Hal was diagnosed with ALS. His 2013 BitcoinTalk post "Bitcoin and me" describes typing with eye-tracking software while still writing code. He died in August 2014 and, as he had chosen, was cryopreserved.
Why he matters
Hal showed that Bitcoin's first users were not speculators but people who wanted money that no one could shut down. He moved his coins to an offline wallet stored in a safe deposit box for his children – an early example of planning an inheritance around keys.