Son of the most minor lord in Westeros, Petyr is a man of pure ambition. He was fostered at Riverrun among his social betters, and fell in love with Catelyn Tully, who did not return his affection. His impropriety got him humiliated in a duel with Brandon Stark and thrown out of Riverrun. Determined to climb the social ladder, Petry used his financial brilliance to become King Robert's Master of Coin and acquired a substantial personal fortune as well. Not content with mere riches, Petyr has become quite the manipulator, working behind many powerful players, but few seem to grasp the full scope of his own ambitions, and even then they might be incorrect. Petyr is called "Littlefinger" due to his short stature and the small strip of land he inherited in the Fingers. Almost everybody looks at his relatively impoverished background, the lack of sworn swords and other inherited resources and, assumes he's relatively harmless, desperately needing their patronage just to survive, but he is obviously playing this to his advantage.
Its said that he used to be a rather sweet, with a mischievous, bold and idealistic personality as a child, that was constantly look down by everyone due to his small and insignificant status, that was struggling to rise above his lowly birthright and become something greater. When he fell in love with Catelyn Tully, he would challenge Brandon Stark to a duel for her hand. However Brandon, being a master swordsman and experienced soldier, soundly defeated him. Because of this, Petyr turned a grim, cynical and unhiged person that he hides beneath a cheerful and upbeat smile.