Coremus was born during the fifth year of Panem's Imperium. Since Coremus was an infant the job of caring for Panem fell on Remus's advisers. They did a fair job, but each one was looking for a way to usurp the current power and become ruler him/herself. A plot to assassinate the President and his son was leaked to Remus by a loyal servant, and he snapped out of his melancholy state and took charge again.
The would-be usurper (a member of the Stone Family, one of Messalina's ancestors) was publicly executed and all those who assisted him were put to death privately. Coremus inherited the office after his father died at the ripe old age of 93. 29 and very serious for his age, the new President set about continuing to run the country with the same efficiency and fairness as his father had. He had a wife, Calista, who gave birth to their first child, Coralista within a month of him taking office. Five years later she was joined by a little brother, Calemus. For the first decade of being President Coremus did his job exactly as his father had taught him, but over time his fatal flaw of greed began to surface. A vicious miser, he saw that the cost of making and sending adequate resources to the out-lying Districts was more than he wanted to spend. Of course they were expected to keep producing their end of the bargain. While things did not go to hell in a hand-basket under his watch, he planted the seeds of discontent.
For one thing, Coremus was not blessed with the beauty his parents had possessed, and Calista was often described as having a lizard face. For another, they knew next to nothing about each other except all the bullshit hype their respective families had fed them over the years. Coremus had been somewhat overprotected since an assassination plot against him and his father had been squashed in his boyhood, so he had the social skills of an angler fish. Calista wasn't a bad person in general, but she never let go of the resentment she felt toward her husband and both their families for duping her into the arrangement.
Coremus took over the country at age 29 and eventually began tweaking the figures for distributing goods and resources to the Districts in order to keep more wealth concentrated in the Capitol. The changes were not drastic, but his short-sighted greed set in motion the events that would lead to the future poverty and starvation that Katniss and her people would deal with.
In spite of their animosity toward each other Coremus and Calista had two children, Coralista and Calemus. Coremus was not a very active father, but Calista preferred to look after her children directly rather than have a nanny do it. It provided her some joy in her situation.
Coremus died at age 54 of pneumonia complications. He was an avid hunter, stocking the mountainous wilderness not far from the city with game that he and some fellow aristocrats would go hunt. Weather was never a hindrance from sport. One day a freak ice storm developed and he was not prepared with the right clothing, and he fell ill after the trip and died. After dying of pneumonia at age 54, Coremus passed his legacy on to his 24 year old daughter Coralista.