Pycelle

""All I did, I did for House Lannister! Always! Your lord father, ask him! I've always been his servant, since the days of the Mad King!"   ―Grand Maester Pycelle, to Tyrion Lannister[src]"

Maester Pycelle is sycophant who dabbles in poison and politics. He serves Lannisters. He's cunning and wily man. He knows how to act in politics despite being dislike by many in King's Landing. He is responsible becaus he advise mad king Aerys to open gates, thus Aerys was slain by Jaime Lannister. He was remvoe from his post when he was assasianted by Qyburn's little birds.