Petrus Alphonsi
Petrus Alphonsi or Petrus Alfonsi (1062 - 1110) was a convert from Judaism to Christianity and a writer and physician.
Wikipedia clams that he is of enormous importance in the development of anti-Semitism, despite not even being mentioned in certain encyclopedias. The Jewish Encyclopedia states that his criticisms are "little known to-day" and "fully merits the oblivion into which it has fallen".
