Ptolemy I (also Ptolemaeus or Tolomeo) (died 1126) is the count of Tusculum in the first quarter of the twelfth century.
He is a son of Gregory III.
Peter Pisanus, in his Vita Paschalis II,refers to Ptolemy and the abbot of Farfa as the allies of the emperor in the same way that the Saints Peter and Paul were the allies of the pope.