Hint: a man who started life with one name but later adopted the one he is today remembered as.
No, not James Joseph Sylvester, the English mathematician initially denied recognition and university degrees in his home country on account of his Jewish background (Trinity College in Dublin obliged with BA and MA in 1841), who had a big impact on the history of mathematics in the USA before finishing his career at Oxford.
We refer to a much earlier Sylvester, known as Sylvester II. Confused?
Born Gerbert d’Aurillac in France, this fellow became Pope Sylvester II in 999, and died this weekend past in 1003 (clearly not in his prime, arguably that had last been in 997)
See “A mathematician who became Pope“ for more on this fascinating man’s life.