Who is Prince Po of Lienid from Graceling and what is their importance?

Prince Po of Lienid is the friend and then lover of Katsa. He is presented as a Graced fighter, with one gold and one silver colored eye. Later, it turns out that he has been concealing that he is really a mindreader and seer. He used his mindreading power to figure out the moves of his fighting opponent and thereby was able to win his fights. Prince Po gets Katsa to do fighting drills with him and becomes her friend. After he tells Katsa that she has the ability to survive and defy King Randa, Katsa hits Po and nearly breaks his jaw. Despite this, after Katsa defies King Randa, she agrees to go with Po on his quest for the true kidnappers of his Grandfather Tealiff. Po uses his mindreading power to figure out that King Leck of Monsea is the one who ordered Grandfather Tealiff kidnapped and that Leck has the power to make most people believe anything he says. Po is able to attack Leck, but fails to kill him and is wounded. When he returns to Katsa, he falls with his horse into a lake and is severely wounded again. Po becomes blind, but uses his mindreading and sensing power to appear to continue to be able to see. Only Katsa is able to see through this facade.