Markov the Gadfly
A slide from a talk by Brian Hayes on the history of Markov chains.
It amuses me to no end that parts of Markov's seminal work on dependent sequences were done to disprove speculations by Nikita Nekrasov on how probability theory can be used to 'prove' free will.
Earlier seminal work in probability theory related to similar theological / philosophical questions. For example, Pascal's famous, but misinformed, wager.
I suppose this speaks some to the usefulness of the ideas of theologians and philosophers: at least on occasion they lead others to deep mathematical insight, if only through aggravation.
Also, I now have even more respect for Andrey Markov.