Yvo Desmedt
Belgian cryptographer usually credited as the father of threshold cryptography: the idea that a private key can be used without any single party holding it.
Shamir's secret sharing (1979) could split a key, but using it meant putting the pieces back together – at which point the key exists in one place again. Desmedt framed the problem of group-oriented cryptography in 1987, and in 1989, with Yair Frankel, presented threshold cryptosystems in which any t of n parties jointly decrypt or sign without the key ever being reassembled.
It sounded academic for thirty years. Then cryptocurrency wallets with multiple signers arrived, and threshold signatures became something NIST wanted to standardise.