I was privileged to know all three of Berlekamp, Conway, and Guy, and I mourn their passing.
From his wikipedia page:
Known for: Surreal numbers, Conway groups, Monstrous moonshine, Doomsday algorithm, Look-and-say sequence, Icosians, Mathieu groupoid, Free will theorem, Conway chained arrow notation, Conway criterion, Conway notation (knot theory), Conway polyhedron notation, ATLAS of Finite Groups, Conway's Game of Life.
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