Conway discovered three new sporadic finite simple groups in the late 1960s, the Conway groups named after him, when he was studying the Leech lattice. He also simplified the construction of the last and largest sporadic group found, the "monster" (but preferred by the discoverer to be called "friendly giant"). In a famous work with his doctoral student Simon Norton from the late 1970s he pointed to the connections between the (dimensions of the irreducible) representations of the monster and the expansion coefficients of the elliptical module function, called "monstrous moonshine" after the title of their essay (she followed an observation by John McKay). Many of the suspected connections were later proven by Conway's PhD student Richard Borcherds, who received the Fields Medal for it. With his research group in Cambridge, Conway published the Atlas of Finite Groups.
