Sarah Meiklejohn
The cryptographer who showed Bitcoin is pseudonymous, not anonymous — by buying things and following the money.
In 2013 Meiklejohn and colleagues at UC San Diego, among them Stefan Savage, published A Fistful of Bitcoins. The method was hands-on: they made hundreds of transactions with known services to tag addresses, then combined that with heuristics — for instance, that change addresses and addresses spent together as inputs belong to the same owner.
The upshot was that large parts of the Bitcoin flow could be tied to exchanges and marketplaces. The paper became the foundation of the entire blockchain-analytics industry and of the investigations around Silk Road and Ross Ulbricht. It also gave a tailwind to currencies such as Monero, built precisely to frustrate that kind of analysis. Meiklejohn later became a professor at UCL.