Émile Borel (1871–1956) was a French mathematician, and one of those maddening people who seem to be brilliant at absolutely everything. He helped build modern probability, dabbled in game theory before it was cool, and — for good measure — became a government minister and a Resistance hero. A child prodigy who never really stopped.
Before you can talk about the probability of an event, you need to agree on which collections
of outcomes even count as "events." Borel's answer was the family of
Borel is the man behind the famous "infinite monkey theorem" — the thought experiment that a monkey hitting keys at random for long enough will, eventually, type out the complete works of Shakespeare. He used it to make a serious point about how events with a tiny probability behave over the very long run. Away from the blackboard he lived several lives at once: member of parliament, government minister, and during the Second World War, at over seventy, he joined the French Resistance and was arrested for it.