Who is Plutarch Heavensbee from Catching Fire and what is their importance?

Plutarch Heavensbee is the Head Gamemaker. He attempts to tip Katniss off to the clock design of the arena, but she misses his point until Wiress continuously repeats tick, tock. Katniss later learns that Heavensbee and Haymitch have plotted a way to help Katniss and Peeta survive the games.