sebastian stan was born in a small town in the island of Jeju where his father (hades) met his mortal mother. it was just around the time when the gods were discussing about not having any more demigod children since it had become a great challenge on how to keep everyone in the lineage from harm's way.

like any other demigod child, Sebastian was brought up by his mom alone until he was 4 years old when some of his powers (inherited from hades) started to appear. having one mortal parent wasn't enough to control him or at least just keep an eye on him and so when he reached the age of 5, his mother found a human partner that she could have to help in taking care of sebastian.

everything was going smooth until he was 13 years old, their family moved in Seoul to start a food delivering business, but sebastian's mother died when Zeus struck the apartment they were staying in with lightning in an attempt to kill sebastian, thinking he was too dangerous. however sebastian and his then step-father were protected by hades as he erected an impenetrable wall of black energy to shield them from zeus' bolts, but hades was not able to protect his mother in time. (canon nico di angelo)

afterward, a devastated hades ordered to take sebastian to the underworld, explaining to him that he is a demigod, son of hades, prince of the underworld and soon after sent him to camp half-blood where he could be safe from other beings and future attacks.

sebastian graduated in the human world with a degree in fine arts and had successfully supported his step-father with their previous food delivery business and also establish his own art gallery.

to this day, he is a full-time camper at camp half-blood and is an armory auditor, making sure that they have a complete and newly dated set of weapons for practice and actual battle.

growing up, sebastian always felt like a gloomy cloud was always following him. no matter how happy everyone around him, he'd just casually offer a faint smile and that's it.

he was deemed 'weird' in the human world and so he didn't really develop a sense of friendship.

he is not someone to celebrate things and be joyous in general. he likes solitude and prefers to be alone... an introvert if you will but would most likely to interject witty comebacks or deprecating humor when forced in a situation he is not comfortable in.

usually comes off with an egotistic to arrogant vibes but that's just because of his resting face.

he has a reasonable temper but don't mess with him, he'll lash out on you and that's a fact.

sensitive to parent/family talks.
 

dark and twisted humor is his forte when he's comfortable hanging around you.

painting is his outlet when he is happy while he tends to train harshly when his mood is not that great.

is greatly interested in the new technology to which he'd find a way to incorporate on several armors, that's his hobby.

has a mild fear of thunder and lightning brought by the death of his mother (refer to background)

very calculative but would rather keep any information to himself unless asked.

likes wine, cheese, night, and cool-airy environment. tarts or any pastry with blueberries is his thing. 

pet-peeve is when someone touches him or anything that belongs to him without his permission (would most likely freak out or glare at you)