Some will know Conway via is work on the Classification of Finite Simple Groups (with many others), some via his "Look and Say" sequence, while still others will know his book "Winning Ways"[2], written with Richard Guy[3] and Elwyn Berlekamp[4]. My copy signed by all three is something I treasure.
I was privileged to know all three of them, and I mourn their passing.
[0] https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life
[1] https://www.theguardian.com/science/2015/jul/23/john-horton-...
[2] https://en.wikipedia.org/wiki/Winning_Ways_for_your_Mathemat...
[3] https://en.wikipedia.org/wiki/Richard_K._Guy
[4] https://en.wikipedia.org/wiki/Elwyn_Berlekamp
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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