Stuart Haber
The cryptographer who, with Scott Stornetta, invented the linked hash chain for timestamping — 17 years before Bitcoin made the same idea famous.
In 1991 Haber and Stornetta, both at Bellcore, published How to Time-Stamp a Digital Document. The problem was proving when a document existed without having to trust whoever applied the stamp. Their answer: each new stamp includes the hash of the previous one, so any after-the-fact change breaks the whole chain. In 1993, together with Dave Bayer, they refined the scheme with Merkle trees so that many documents could be stamped at once.
To make the chain public they founded Surety, which since 1995 has published a hash every week in a classified ad in The New York Times — a blockchain printed on newsprint and archived in libraries. When Satoshi Nakamoto wrote the Bitcoin white paper in 2008, three of its eight references were to Haber and Stornetta.