Paul is famous for his essay about Lisp - arguing that his startup beat other startups because Lisp is such a better language than C++ or Java which his competitors were using.

Unclear to me if this is really the meaningful reason that Paul's company succeeded (I'd say obsession with programming languages can be a counter-indicator for productivity), but it clearly resonated with a lot of people since that essay is arguably the onramp into Paul's fame. A lot of programmers read that essay back in 2001. His popularity as an investor who understood engineers arguably catapulted YCombinator