British cryptographer and CEO of Blockstream who invented Hashcash, a proof-of-work system that informed Bitcoin's design. Back appears in thousands of DOJ-released Epstein files because Epstein invested approximately $500,000 in Blockstream's 2014 seed round through Kyara Investments III, a vehicle co-owned with former MIT Media Lab director Joi Ito. Email records show Back and co-founder Austin Hill corresponded directly with Epstein about the funding round, which was oversubscribed at $21 million total.
A separate email from Epstein to early Bitcoin developer Amir Taaki claimed he had recently hosted "Andy Back" on Little Saint James island, though whether this refers to Adam Back remains disputed. After the DOJ released files in early 2026, Back stated publicly that Epstein's financial stake was divested after just a few months and that no ongoing financial relationship existed. Bitcoin developer Luke Dashjr called on Back to resign.
Back denied any ongoing relationship with Epstein.