When you want it, you will not find it.
If you try to use it against its will, you will fail.
When you have neither want nor use for it - then it is yours.
Stephen holds the world's lost artifacts within his home. He's one step away from being a dragon in terms of how he hoards things, and while there is an abundance of his shown wealth (by way of paintings and old books) there is so much more hidden away that no one gets to see. Things tend to find him and he rarely goes out to find it, with the exception of the three months when the urge to seek out something rare overtakes him, and then he will go to the ends of the Earth to make sure that it's his.
He is no stranger to the artifacts of other races, he is, like so many Templars before him, a banker - someone that holds things safe for others but demands a fee to keep it. [In fact, he holds that the best bankers are actually dragons, but that's mostly a joke that he has with a certain Silver.] It's with him that the Tuatha de Danann have entrusted with their sacred weapons while they are held in exile in a parallel world. He harbored art from the great wars and books from the pyre. And sleeping survivors from planets whose name he'll never be able to say. His home is built upon a vortex that negates minor magic, and even most technology struggles to work within its boundaries (for what is technology but magic made mundane?), but such is the power of the Collector (though he'd never see it as such).
Stephen has become something of a fixed point, a central figure for those who wish to hide something (or someone) within a land that is set apart from time, like he is set apart. He is the wise hermit, the quest-maker, the one who knows -with just a look- what item (or person) wishes to go with the stranger in front of him. He was a knight by training, made immortal without consent, and he struggles to reconcile his faith with what he's become but just because he was cast out of his order doesn't mean that he won't forever be loyal to it and to his God, though he's learned - painfully - that Good and Law may not always be one and the same, just as his Church and God may not be one in the same.
He is the Collector, first and foremost. He is the protector of those that come into his care and for all that he's removed from those that visit, that stay with him for a time, he's fond of them in his own way. At nearly eight centuries old, he's lost many, and grieved with each passing, and what he's come to collect: books, paintings, tapestries, magic relics, it matters not - they've all hold some memory attached to them, and the power that he will use selfishly, the only power that his Guardian has permitted him ready use, is the ability to call up a Whisper [he calls it a Fragment] of the artifact, a manifestation of the sentience that resides within it, and he gives it shape, a voice, and through continued teachings by the Whisper, it gains a humanoid shape, though it's never strong enough to do more than speak to him for an hour at the most before it fades away to rest again.
Stephen had been raised as a warrior in defense of the Church and its people, now, he is a warrior in defense of the ancient relics and cultures of those that come into his care because he is of the belief that God resides in all things, not just in those given a name by the Book he swore by, and it need not have a name and it may be an 'enemy' of the Faith, but... so he is, if one believes the Brothers who tortured him and tried to kill him for a deed visited upon him by a man he loved above most all things.
How did it happen? Him becoming the Collector? The knowledge that he had neither need nor want for any power, no ambition to rule anyone, no desire to use anything (or anyone) that came into his possession. He's a placeholder, a place of safety, someone who may grow to love something (or someone) he has, but knows when he has to let it (or them) go. it's eight centuries of sacrifice to make up for the lives he's taken and the sin he (unknowingly) committed.
