Jack Frost is a supernatural being much like the Guardians. But unlike the others he is a loner, the classic rebel without a cause. He is a teenage hellion who has no interest in being bound by rules or obligations and just wants to use his staff to spread his winter magic for the sake of personal amusement.
The source of his anti-social behavior towards the Guardians and refusal to ad here to rules was mostly because of his frustration with the Man in the Moon never answering his questions about who Jack was or why the Man in the Moon created him, and also because no human, child or adult, was ever able to see him for centuries since no one believed in him. But as he spends time in the company of the Guardians, each of them would have an effect on him that would change him from a mischief-making winter spirit to a full-fledged Guardian in his own right, as well a hero.
It was his refusal to give up in the face of overwhelming odds that enabled him to help one child, Jamie, to keep his beliefs in all of the Guardians as well as finally believe in Jack enough to see him.
H-Canon Jack Quotes
"I may not be a saint but at least I am bold enough to call you out on your BS."
"I think of a few ways you and I can pass the time. . .SHOPPING!"
"Don't call me kid, I swear I. . .I'll do something."
"I'm freaky in the best kind of way."