This refers to Michael Pemulis, the school's first master of Eschaton, a game described in an endnote as "a real-participant and tennis-court-modified version of the EndStat ROM-run nuclear-conflagration game." Played by 12-14 year-old E.T.A. students, it is a computer-aided turn-based nuclear wargame, combining military strategy and precis lobbing. The game takes it's name from the word eschatology, the branch of theology that is concerned with the end of the world or of humankind.
The concept of Eschaton may have been influenced by the Don DeLillo novel End Zone, which tells the story of American football player Gary Harkness, who has an interest in nuclear warfare and makes frequent mention of the word 'eschatology'.
Here is a full breakdown of Eschaton's history and rules.
Read here for an excellent article on how a group of students once staged a play largely based around a game of Eschaton.