Plutarch is the new Head Gamemaker for the Quarter Quell. It's ballsy to take up that position after the last guy was executed for permitting both Katniss and Peeta to live, but Plutarch doesn't seem to have a problem with it. And his arena is, if anything, even more lethal than the one from the previous Hunger Games. It's the Quarter Quell, after all – gotta kick things up a notch.
Plutarch's inventions are so brutal that later we're surprised to learn that he is on the side of the rebels, and has been all along. If he's trying to save the Quarter Quell tributes, why did he have to go to such lengths to make the arena so deadly? To preserve his status in the Capitol and keep his cover intact?
But Katniss would have realized that there was more to Plutarch than met the eye if she'd known to look for the signs. When she met with Plutarch at a grand event on the Victory Tour, he gave her a hint, which she begins to decipher once she's begun to understand the arena itself:
I see a clock. No, it's a watch, resting in Plutarch Heavensbee's palm. 'It starts at midnight,' Plutarch said. And then my mockingjay lit up briefly and vanished. In retrospect, it's like he was giving me a clue about the arena. But why would he?" (23.9)
The last thing to remember about Plutarch is how savvy he is. He's the Head Gamemaker after all, which means he's a strategy beast who can outthink and outplan the best of them. He understands media and popular culture, based on his analysis of Katniss as the face and embodiment of the revolution. In our opinion, the revolution is lucky to have him.