921 AARON BEN MEIR (Eretz Israel)
Leader and sage. He devised a change in the calendar, and as part of his efforts to reinstate Palestinian control over the calendar, he reinstated the tradition of proclaiming the new moon from the Mount of Olives. This caused confusion regarding the date of Passover. Sa'adia Gaon, aware of what a split would do to Jewish unity in the face of the Karaite division, nevertheless wrote a refutation called the "Book of Seasons". The underlying issue was one of supremacy in Halachic rulings - Babylon or Eretz Israel. Sa'adia won and received the Geonate of Sura in recognition.