Clue 1: I was a general and a politician who was born in Rome in 100 B.C.
Clue 2: In 45 B.C., I introduced the Julian calendar. It had an extra day every fourth year--a leap year.
Clue 3: Changes were made to create the modern calendar. But leap year still happens every four years, with an extra day at the end of February.
Who am I?