Although no-one really knows who Satoshi Nakamoto is, we do know that he (or she or they) created the bitcoin protocol, publishing the whitepaper in late 2008 and then releasing the first version of the open source software client in 2009.
Satoshi Nakamoto was active in the development and testing of the bitcoin software until mid-2010, being the only one to make modifications to the software up until he handed over control of the source code repository to Gavin Andresen. The last public communication he had was in early 2011 when he said he had "moved on to other things".
Much discussion and debate abounds regarding the true identity of Satoshi Nakamoto. Over the years there have been many attempts to find out who this person really is, but no hard evidence exists that it is any one person in particular. Judging from his name, it would be logical to assume that Satoshi Nakamoto was Japanese. But lots of circumstancial evidence suggests otherwise, pointing to the fact that he used perfect English in all his communication, and the bitcoin software was not documented or labelled in Japanese. Other research concluded that he probably did not live in Japan due to the timing of his bitcoin forum posts which showed little to no activity between the hours of 5am and 11am GMT, suggesting he was asleep between those hours.
Besides a random Japanese gentleman named Dorian Satoshi Nakamoto (who coincidentally lived in the same neighbourhood as Hal Finney), most of the speculation regarding his true identity has pointed to one or more of the original cypherpunk group as likely suspects; Hal Finney was a possible candidate put forward by Forbes Journalist Andy Greenberg in an article published in early 2014, and Wei Dai has been named as a possibility in many online forums. Probably the best article I have read is by New York Times reporter Nathaniel Popper written in 2015 in which he expands on the most plausible theory that Nick Szabo is Satoshi Nakamoto after he was linked to the Bitcoin whitepaper in an article from late 2013 by blogger Skye Gray through forensic linguistics analysis.
The first bitcoin was mined by Satoshi on 3rd of January 2009, and since he was the sole miner he continued mining bitcoins for about 10 days. Every time a new block was mined, a new public/private key pairing was created, so effectively a new wallet was created every 10 minutes, each with 50 new bitcoins in it. These first few thousand bitcoins are still in the original wallets and remain unspent and, according to the public blockchain, there are roughly 1 million coins residing in these wallets equivalent to over US $6 billion.
On the 12th of January 2009, Satoshi created the first bitcoin transaction by sending 10 bitcoins to Hal Finney. Other notable firsts were recorded on the 12th of October 2009 when the first trade of bitcoin for fiat currency took place, and on the 17th May 2010 the first recorded purchase with bitcoin was made when bitcointalk forum member Laszlo bought a pizza for 10,000 bitcoins. In today's market, those coins are now worth US $60 million.
The question of who Satoshi Nakamoto may be is ultimately a moot point. The fact that he is of indeterminate state just complements the overall decentralised ideaology of Bitcoin in that there is no "leader" of the movement,. Almost 10 years since the inception of Bitcoin, the reality is that the participants in his dream are the ones that will help to make it successful.