Ptolemy I (Latin: Ptolemaeus or Italian: Tolomeo; died 1126) was the count of Tusculum in the first quarter of the twelfth century.
In 1111, the Emperor Henry V imprisoned the pope and some of his cardinals in Rome and Robert I of Capua sent 300 men to rescue the papal entourage.
In March 1116, the Roman Prefect Peter died and Paschal appointed a son of Pier Leoni as his replacement.
At this point, his son was also titled count and this younger Ptolemy was given in marriage to Bertha, illegitimate daughter of Henry.
On 5 February 1105, after wars with Gaeta, Ptolemy had confirmed by a treaty the safety of the Gaetan traders in his domains.