A math theorem called the Road Coloring Problem, first conjectured by Benjamin Weiss and Roy Adler in 1970 was finally solved in 2007 ... by Avraham Trakhtman, a mathematician who worked as a night watchman after he immigrated to Israel:
“In math circles, we talk about beautiful results — this is beautiful and it is unexpected. Even in layman’s terms it is completely counterintuitive, but somehow it works,” says Stuart Margolis, a colleague who recruited Mr Trakhtman to Bar Ilan University near Tel Aviv. [...]
[Stuart] says the discovery was especially remarkable for two reasons. “Math is usually a younger person’s game, like sports,” he says. “Usually you do your better work in your mid 20s and early 30s. He certainly came up with a good one at age 63.”
Secondly, Trakhtman has an unlikely background.
“The first time I met him he was wearing a night watchman’s uniform.”
Originally from Yekaterinburg, Russia, Trakhtman was already an accomplished mathematician before he came to Israel in 1992, at the age of 48.
But like many immigrants in the wave that followed the breakup of the former Soviet Union, he struggled to find work in the Jewish state and was forced into stints working maintenance and security before landing a teaching position at Bar Ilan in 1995.