Caligulanus grew up in a very wealthy family, and was born in in 57 PI. He started to rule Panem when he was 25 years old. He is said to have poisoned his mother so he could take the throne, but this can't be confirmed.
He cared less for running government than he did for satisfying his own sick pleasures. Rations to the Districts were cut dramatically, leaving thousands of people without enough food to survive. When asked why he did such a thing he simply replied "because I can." He would send hovercrafts to the Districts and abduct young people, usually between the ages of fifteen and twenty, and have them brought to the Presidential Manor.
Even up to the death of Coralista and the ascension of Caligulanus, Lilith and Drusus were still very much in love. Caligulanus, being a sick son of a bitch, decided he was going to steal Lilith (who was twice his age) from his father. However Lilith was no wimpy thing. When she was brought into Caligulanus's bedroom she smashed a mirror with her fist and attempted to attack the new President with one of the shards. She was shot twenty-eight times by his bodyguards and died on the scene.
The prettiest ones he would add to a slave harem he began in his second year as President. The strongest ones he would force to fight to the death in the throne room for his amusement. He took no wife and fathered no children, as he didn't care for that, so his sister Corlana was heir presumptive to the throne. She already had a hand in running the government since her brother was often to deep into drug binges and orgies with his slaves to do it himself. She shared his opinion that a good government had to be feared in order to be respected, but she frowned upon his personal life. The Dark Days started three years into Caligulanus's reign and continued for the rest of it. Hungry citizens' outrage was compounded by news of the President's depravity, and open rebellion ensued. Caligulanus died of alcohol poisoning in his bedchamber at the age of 37.