He's just one of several candidates[1], although I think the late Hal Finney is more likely to be Satoshi.
Another theory is that the Satoshi persona was created by a group of individuals (cypherpunks) who were involved in the early Bitcoin community, including Hal Finney and Nick Szabo.
[1]: https://en.wikipedia.org/wiki/Satoshi_Nakamoto#Possible_iden...