Markus Jakobsson
Cryptographer and phishing researcher who, with Ari Juels, coined the term "proof of work" in 1999.
Making a client pay in computation was already in Dwork and Naor's 1992 paper, but it was Jakobsson and Ari Juels who named it, in Proofs of Work and Bread Pudding Protocols (1999). The bread pudding was about recycling work already done into something useful. A decade later proof of work became the backbone of Bitcoin, minus the pudding.
Jakobsson has worked at Bell Labs, RSA Laboratories, PARC and PayPal, and spent much of his career on the human side of security. He co-edited Phishing and Countermeasures (2006), one of the first academic books on phishing, and made a habit of measuring how easily people are fooled rather than assuming it.