Bitcoin
First decentralized cryptocurrency. Anonymous creator "Satoshi Nakamoto", white paper October 2008, genesis block January 2009.
Proof of Work consensus (SHA-256). Max 21 million BTC, reward halving every ~4 years (latest April 2024, now 3.125 BTC/block). Drives enormous energy use (~150 TWh/year, comparable to some countries). Lightning Network is layer 2 for small payments. Bitcoin ETFs approved in the US January 2024. "HODL", "stacking sats", "not your keys not your coins" are cultural memes.