Aemon

Aemon is a character in Game of Thrones. The actor playing him has not been announced yet, but he is expected to appear in the first season.

Aemon is the maester at Castle Black and is one of Lord Commander Mormont's closest advisors.

In the books
In the Song of Ice and Fire novels Maester Aemon is a hundred years old and widely-believed to be one of the oldest living men in all of Westeros. He has been on the Wall for sixty years and is known for his great wisdom, wise counsel and trusted judgement.