Hal Finney
In short: Hal Finney was an American cryptographer and programmer who, along with Satoshi Nakamoto, pioneered the development of Bitcoin.
Hal Finney was an American cryptographer and programmer who, along with Satoshi Nakamoto, pioneered the development of Bitcoin. He was one of the first people to run the Bitcoin software and help test the young network.
Why it matters
Before Bitcoin, Finney was a respected figure in the cypherpunk movement, which promoted privacy through cryptography. He worked on PGP, one of the best-known email encryption programs, and created RPOW, a "reusable proofs of work" system that explored digital cash built on proof-of-work. When Satoshi Nakamoto released Bitcoin, Finney downloaded it early, mined some of the first blocks, reported bugs and discussed the design with Satoshi. That early support helped show that the system worked in practice. He was later diagnosed with ALS, a disease that gradually paralyzed him, and he kept programming with eye-tracking software. Some people have speculated that he was Satoshi Nakamoto, but he denied it.
Example
The first known Bitcoin transaction between two people was Satoshi Nakamoto sending 10 BTC to Hal Finney as a test. It is recorded in one of the earliest blocks of the Bitcoin blockchain, and anyone can still look it up with a block explorer.