Backstory
Grisia was a particularly foolhardy young silver dragon, and he wanted to see the world with his own eyes long before he was old enough to cast Change Shape. Despite being discouraged from doing so, with all the confidence and pride of a teenager AND a dragon he did so anyways.
Even still, Grisia was not stupid, and he had a pretty easy journey so long as he took care to avoid any large cities or settlements. With his great wings, he was able to cover much ground, and explore more of the world than most humans could dream of seeing in their entire lifetime. There was one place, however, that even with the greatness of flight he could not traverse, and of course that which was most inaccessible was most tantalizing. This place, was of course, the Underdark.
Grisia spent a great deal of time, his curiosity wrestling with his logic, before his curiosity won out. So, Grisia voluntarily trapped himself underground, and walked into what would be a very unique life for a dragon.
For awhile, everything was smooth, for there were very few creatures willing to challenge even an adolescent dragon, and those so foolhardy quickly could be met with an icy demise. He was a little disappointed in this, as it allowed him less creatures to investigate, but he still was finding the excursion enjoyable. Less enjoyable, however, was what came next.
Unknowingly scrabbling just a touch too close to a Drow city, the following patrol could not miss the signs of such a large creature nearing the city, and set out on a hunt. Originally intending to slay the creature, upon realizing that it was, in fact, a young dragon they instead became intent upon capturing him. Even a single scale of a dragon was of immense use and worth, an entire dragon would be an unbelievable bounty indeed.
It was a long hunt, with many losses on the side of the Drow, many days and many calls for reinforcements, before Grisia was worn down enough to be captured. Nearly.
Nearby Drow rebels had caught wind of the hunt, and saw in it their chance to take down many more of Lolth's faithful. As the rebels heard the fighting come mostly to a halt, they struck. It was not hard for the rested and fully prepared rebel drow, to defeat a weakened and burdened party of even the greatest warriors with a well timed ambush. The battle was over hardly before it began.
Even the rebel Drow would not trust a dragon, but nor could they leave him where he was in his weakened state, knowing that doing so would just put him right into the hands of the city Drow yet again. Trusting that the dragon was weakened enough to not hurt them if worst comes to worst, they sought a temporary alliance. Despite their distrust, they Drow did not miss the potential for a very powerful ally.
Neither could Grisia trust the Drow, but he recognized that he had little other options. So truly began his life in the Underdark.
Grisia stayed with the rebel Drow as he was healing, and after recognizing them as mostly genuine in their intentions, his curiosity about the Drow people had him staying even after that. Grisia learned far more of the Underdark from the mouths of it's people than he ever could have from even the most careful of individual observation. Originally an alliance of necessity, Grisia and the rebels eventually grew to be endeared to each other. Grisia stayed with the Drow rebels into his adulthood, and finally able to change shape, Grisia decided to take the form of a Drow himself in honor.
Grisia could not live confined to the underground forever, however. He recognized this experience as unique and valuable, but his soul yearned for the skies. So, Grisia said goodbye to the rebel Drow, his friends, and took to the surface for the first time in over a decade, still donning the form of a Drow, ready to meet the rest of the mortal world.
Upon realizing the bias against Drow on the surface, but stubbornly refusing to take the form of anything else, Grisia decided instead to take advantage of the intrigue he brought. Mimicking the style of craft he remembered from his time in the Underdark, he took on the persona of a Drow dissenter trying to make a living on the surface, selling crafts from his "homeland" and used that to make his living in the mortal world. Using this money, of course, to buy any treasures that caught his fancy.
Grisia now continues to travel throughout mortal society, with his gaudy merchant's cart and his trusty steed, making his fortune and immediately spending it.