Abraham Abulafia had a terrific, if a tad unorthodox, idea. Let's convert the pope to Judaism!
Abulafia wasn't just an average crazy person. He was a 13th century philosopher and Kabbalist. He also passed himself as the messiah. So, a non-average crazy person.
Abulafia made the trek to Rome, where he was all ready to meet the pope and... we don't know. Was he gonna try to talk him into Judaism? Give him some delicious Jewish treats like kugel? Convince him with a rousing klezmer melody?
Sadly for Abulafia, the pope was ready as well. Ready to burn Abulafia at the stake.
But Abulafia's fortunes turned. The day before he was to try to convert the pope, the pope dropped dead. No Judaism for him, but not much of anything else either.
And no stake for Abulafia. He was jailed and exiled to Malta, where he was free to preach his Messianism to local rocks and vermin. So much for terrific ideas...