Name: Lao Kai
Race: Ex hengeyokai.
Status: Fallen quasi-deity/dragon ascendant
Gender: Male
Age: Darn hard to tell, but he often jokingly claims to be twenty-one.

[Physique]

He tends to appear as young, human male. Tall or short depending on convenience, but most of the time powerfully built.
Long, white hair and beard make him look a bit like a sage from eastern lands. At least untill his youthful face is seen underneath.

[Behaviour]

A bit melancholic, and easily lost in thoughts, but his natural curiosity and playfulness usually takes the better of him.

[Miscellaneous]

- Can be easily mistaken for a regular true dragon, possessing most of their traits,
- Attempts to interfere with him using magic, poison and curses would most likely fail due to his resistances,
- All of his magic except normal spells is using either his blood, rituals or both.
- Like any dragon, he sees through invisibility spells and hidden people, this ability seem to be exhausting for him in human form.

[History]
TL;DR at the bottom.

As young hengeyokai thrown out of Feywild by magic accident, Kai lived his early years on Prime Material plane,  while being almost unconscious.

His first memory is that of a villager rubbing his scales for luck, common thing to do to lizards as colourful as Du. Silver, gold, blue, green and red, bright and shiny reptile, finding such a beautiful animal was a sign of fortune for the local people.

Plentiful years that followed were quickly attributed to young, animal yokai. Easily gaining reputation of a local guardian spirit.
He travelled across Toril, always coming back to that one, secluded village, which took him in so warmly. Kai always did his best when stumbling upon people in dire situations. Saving drowning people, children about to be eaten by monstrocities, or women kidnapped by bandits. His tiny, local legend grew. People mentioned powerful, whitehaired figure appearing, when a good person needed it the most.

Such worship couldn't come without effects on yokai himself. Hailed as Lao-Kai, he came to be praised as protector deity in that, now big town.
Hengeyokai should be able to change into one animal and human form, maybe something in between, and he already put on too many faces to remember them all. From various critter, on dragons ending. That last shape, a giant wyrm changing colour as he sees fit,  becoming in the end his most known aspect.
Going on journeys, often lasting few decades, after all that time, he finally realized that he "might've been around for a while".

Even more years passed, and the travels have finally tired him for the time being. Playing pranks didn't bring him satisfaction anymore. His people, the thing that kept him in this remote, self-sufficient city, were doing well on their own. Lao Kai was not needed for now...
...it was time to rest.

Countless years passed, before he finally awoke from his slumber. Something was not right. That feeling accompanied him from secluded, hidden lair, all the way to his city.
...or rather the place, that the city once occupied. Forest spread throughout ruins of once bustling town, claiming most buildings, except the biggest one in the center.
Signs of battle all over the rubble told him, that there was nothing alive waiting for him inside. A broken statue of dragon greeted Kai with warped, sarcastic smile. Partially crushed stone tablet lying before it, had hastily carved out letters almost completely eroded.  But accusation of being abandoned was still visible, painfully clear.

With broken heart, and just a twinkle of his divine spark left, he decided to look for a place to start anew. New place to call his own.

TL;DR

He's a shapeshifting yokai coming from the Feywild. Over centuries, he risen to status of quasi-deity, through process of amassing followers and dragon ascendancy. Prankful, whimsical god that Kai was, at some point, he decided to take a break from everything and fall into deep slumber.
Upon waking up, the city he helped establish was long gone,  bones crumbling on the wind. Dire sight bore witness to unknown invasion that happened while he was asleep.
Now, almost completely stripped of his former power, he stumbles around Sinfar, looking for a new place to tend to.