Don Beaver introduced the MLE (Multilinear Extension) to cryptography as a method for privately delegating computations; it became the core trick behind SumCheck and modern proof systems within months [Beaver Feigenbaum 1989]. He's known for other accessible discoveries in cryptography: MPC Triples, Pseudorandom Correlation Generators, Distributed Random Beacons, the "public inverse trick," "real-ideal" security proofs; and for contributions to "garbled" circuits and deniable encryption.