He is a well known Cypherpunk, Cryptographer and widely recognized for his invention Hashcash a protocol that is used to identify email spam and control it. He proposed Hashcash in 1997 which was used by Satoshi Nakamoto, Bitcoin’s inventor, to develop Proof of Work (PoW) consensus protocol.

PoW is used in Bitcoin network as part of mining algorithm. He is also known as one of the first two people contacted by Satoshi Nakamoto for developing Bitcoin protocol.