|Caspar Lucian Blackthorn|
|Mother||Neridah Blackthorn (deceased)|
|Father||Mark Blackthorn (deceased)|
|Ancestor/s||Arthur Blackthorn (grandfather)|
|Significant Other||Jamie Midwinter (parabatai)|
|Residence||New York Institute|
Born on the 19th of November 2015 to Neridah and Mark Blackthorn; named Caspar Lucian Blackthorn. Usually called Cas, at the time of his birth, his older sister, Lucy, was two years old. Lucy wasn't overly fond of her baby brother, and actually injured him several times in fits of jealousy. By the time Cas was one, though, Lucy was over it, and when Cas' younger brother Rye was born when he was three, Lucy was a doting older sister. Cas spent his early years living in the Los Angeles Institute. It was a time he greatly enjoyed.
For several years, Cas had a thoroughly uneventful life, but when he was five both of his parents died suddenly in a car crash. All three children were in the car at the time, but, sitting in the back seat, were protected. It was suggested that the Blackthorn children stay with their large extended family in Los Angeles, but the Clave stepped in, citing a new program that had recently been set up for orphaned Shadowhunters, and sending Cas and his siblings to New York, to live in the Institute there.
When Cas and his brother and sister arrived at the Institute, there were already four children living there - six-year-olds Jon and Merry Fray and their two-year-old sister, Nina, as well as four-year-old Nas Lightwood.
A couple of years later, when Cas was seven, Jamie Midwinter, a boy Cas' age, joined the gang.
Finally, during Cas' eleventh year, Layla Nightshade, a small child of ten, came to live in the Institute.
Cas became very close to Jamie, the two of them being the only boys their age in the Institute, and when they were fourteen the two became parabatai during a visit to Idris.
Shortly before Cas' seventeenth birthday, Karen Lewis, a werewolf, started recieving threatening letters, and in a bid to protect her family, moved into the Institute to live with the rest of them.
Cas has mousey brown hair and very light blue eyes. His bone structure is fine and delicate, from his fairy heritage. His skin is pale and bruises easily. Cas prefers to wear mundane clothes over anything else, feeling that it makes him fit in more. He wore glasses as a child, but got contacts when he was around twelve. He has a scar down his left cheek which he got as a baby when his sister tipped over his high chair during breakfast.
Cas is outwardly the strong and silent type, with a tough demeanor and harsh temper, but when he relaxes he becomes what could be considered unusually quiet and sensitive for a boy of seventeen. He is fond of his siblings, but feels closest to his parabatai, with whom he shares everything. Cas' memories of his parents are faint and growing fainter, something which makes him feel guilty. He knows that Lucy longs to return to Los Angeles above all else, and he also feels guilty that he and Rye are holding her back. Cas would be willing to return to Los Angeles with his sister, but the place he loves the most is Idris, because just being there makes him feel safe.