#BitcoinKeyZone Bitcoin (abbreviation: BTC; sign: ₿) is the first decentralized cryptocurrency. Based on a free-market ideology, bitcoin was invented in 2008 by Satoshi Nakamoto, an unknown person.[5] Use of bitcoin as a currency began in 2009,[6] with the release of its open-source implementation.[7]: ch. 1  In 2021, El Salvador adopted it as legal tender.[4] It is mostly seen as an investment and has been described by some scholars as an economic bubble.[8] As bitcoin is pseudonymous, its use by criminals has attracted the attention of regulators, leading to its ban by several countries as of 2021.[9]