It wasn't even Satoshi who came up with the proof of work mechanism, it's from Hashcash which was invented in the 90s. What he did do though was have the good sense to connect the two concepts!
PoW is not from Hashcash and wasn't invented by Back. PoW was first formally conceptualized in 1992 in the paper "Pricing via Processing, Or, Combatting Junk Mail, Advances in Cryptology" by Cynthia Dwork and Moni Naor. Hashcash was proposed 5 years later, in 1997.
Satoshi is the first one to come up with a way to leverage PoW into a permissionless and global consensus mechanism instead of solely being a cryptoeconomic spam filter.
Satoshi is the first one to come up with a way to leverage PoW into a permissionless and global consensus mechanism instead of solely being a cryptoeconomic spam filter.