Prince of Winterfell
The Prince of Winterfell, was arrogant, handsome and cocksure – very different from whom Theon is now. The Prince of Winterfell has become almost a third person to Theon, he compares himself to him.
A Clash of Kings
Theon takes Winterfell and crowns himself Prince of Winterfell.
A Dance with Dragons
Theon is chosen to ceremoniously present "Arya" in marriage to Ramsay Bolton, since he was the longtime ward of Eddard Stark and it is widely believed that Arya's trueborn brothers are dead. When Theon gives away the feigned Arya Stark to Ramsay Bolton he is made to play the part of the Prince of Winterfell once again.
I am the Prince of Winterfell! This is my seat, no man will drive me from it. No, nor woman either! 
- Theon, to his sister Asha Greyjoy
It had been so long. He was no rider. He was not even a man. He was Lord Ramsay’s creature, lower than a dog, a worm in human skin. “You will pretend to be a prince,” Lord Ramsay told him last night, as Reek was soaking in a tub of scalding water, “but we know the truth. You’re Reek. You’ll always be Reek, no matter how sweet you smell.
– Reek, on his way to Moat Cailin
I made myself the Prince of Winterfell, he thought, and from that came all of this. He had thought that men would sing of him for a hundred years and tell tales of his daring. But if anyone spoke of him now it was as Theon Turncloak, and tale were told of his treachery.
There will be no flaying here whilst I am Prince of Winterfell, Theon had responded, little dreaming how short his rule would prove.
The Prince of Winterfell had been a graceful dancer, but Reek with his missing toes would be grotesque.