John Horton Conway died on 11 April 2020. I found out about this sad news via SMBC. XKCD also has a clever tribute.
Prolific in many branches of mathematics, Conway was a professor at both Princeton University and Cambridge. Despite having an Erdös number of one, he is arguably most famous for his cellular automaton, Conway's Game of Life.
Some years ago Google made an Easter Egg celebrating Conway's cellular automaton; enter "Conway's Game of Life" in a Google search box to see pale blue cellular patterns emerging from the side of your browser's screen.
Image source: "Thane Plambeck" / CC BY