The pseudonym of the anonymous individual or group that created Bitcoin. Satoshi Nakamoto published the Bitcoin white paper in October 2008. They launched the network the following January.
The mysterious programmer continued to be involved in Bitcoin development until their departure in April 2011. In their final message to Bitcoin Core developer Mike Hearn, Nakamoto claimed that they had "moved on to other things."
Like Nakamoto's true identity, no one knows the reason behind the sudden disappearance. However, some speculate that the programmer was becoming uncomfortable with the attention Bitcoin was receiving — notably from the CIA.
Since their disappearance, there have been plenty of rumors about who Nakamoto is or was. A few individuals have also claimed themselves to be Bitcoin's creator. However, no one has ever proved it by signing a message using the cryptographic keys from Bitcoin's Genesis Block or transacting any of the roughly 1 million BTC believed to have been mined by Nakamoto in the network's infancy.