MULLER, or REGIONONTANUS, JOHN, a celebrated astronomer of the 15th century, was born at Koninghoven in Franconia in 1436, and acquired great reputation by publishing an abridgement of Ptolemy's Almagest, which had been begun by Purback. He went to Rome to perfect himself in the Greek tongue, and to see the Cardinal Bessarion; but finding some faults in the Latin translation of George de Trebizond, that translator's son assassinated him in a second journey he made to Rome in 1476, where Pope Sixtus IV. had provided for him the archbishopric of Ratibon, and had sent for him to reform the calendar. Others say that he died of the plague.