Bitcoin was created in 2009 by the anonymous developer Satoshi Nakamoto. It is a digital currency that uses cryptography to control the creation of new coins and verify transactions. Bitcoin transactions occur between users directly without an intermediary. The total number of bitcoins that can ever be created is capped at 21 million. Some key features of bitcoin include that it is decentralized, open-source, peer-to-peer, and allows for fast but irreversible transfers.