Born to the Ray Family, who were only a few shades shy of the Snows as far as social prestige and wealth, he was a master of the art of doing absolutely nothing. Since he was his parents' only child and the rest of his immediate relatives were childless he was set to inherit several fortunes, so he never bothered to become employed.
Most of his life up until his early thirties was carefree and happy. He was a socialite and pretty nice person considering how spoiled he was. The fact that he had no interest in politics and had no agenda to push helped him stay amicable.
But then Corlana's hand in marriage came on the market. As the one who would bear the heirs to the Presidency she was the nation's most desirable bride at the time, and everyone who had half a chance in hell was vying for the privilege. Marcellus's family pushed him hard into courting her, and since he had no ambitions of his own Corlana chose him. The fact that she could appropriate his wealth and property when she became President factored into her decision, but more important to her was someone who would stay the fuck out of her way. Too many of the other hopefuls had political agendas to push and she did not want her "sperm donor" to try and edge in on any of her power.
They actually got along pretty well. They weren't in love or anything, but before Coriolanus was born they formed a decent friendship. When he was born though...
Marcellus died of blood pressure complications at age of 42, when Coriolanus was eight. Basically, the kid stressed him to death. Unless mama laid down the law, young Coriolanus behaved like a hyena on a four-day meth bender. Screaming, hitting, running around, spitting on people, throwing things, cackling like a lunatic, you name it. It didn't take long for word to get around that being the nanny in the Presidential Manor was more stressful than disarming bombs in combat. So by the time Coriolanus was about five and a half no one was around to watch him but his poor father. Marcellus tried, he really did, but he was too much of a marshmallow to command any real authority. The kid walked all over him, sometimes literally. You could say he was Coriolanus's first victim.
The 40th Hunger Games
During this time, he is mentored by Thorburn. She also talks about the cause of death, which was of drinking to much. However, this was a lie to cover up his real death, as mentioned above.