The pizza transaction is the canonical demonstration that Bitcoin could function as money. His GPU mining work also forced early conversations about fairness and the arms race that would define mining.
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Programmer who, on 22 May 2010, paid 10,000 BTC for two delivered pizzas — the first documented purchase of a physical good with Bitcoin, now commemorated as Bitcoin Pizza Day. He also wrote the first GPU miner, dramatically increasing the network's hash rate.
In their words
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“I just want to report that I successfully traded 10,000 bitcoins for pizza. Thanks jercos!”