One Ex Blood Junkie
The above mentioned 'ex blood junkie' is Sam Winchester.
Sam Winchester, the younger of the two Winchester brothers, was born on May 2nd, 1983 in Lawrence, Kansas. His parents were John and Mary Winchester. He is 4 years younger than Dean and was 6th months old at the time of Mary Winchester's death. He was in his crib on the night of November 2nd, 1983 when Mary was murdered by the Yellow Eyed Demon (Azazel) in his nursery. Mary interrupted Azazel who was feeding demon blood to Sam, for a purpose that we do not find out until later. Mary's scream wakes up John and he finds her pinned to the ceiling of the nursery, slashed across the stomach, she then proceeds to combust and burn the house down. Dean, Sam and John barely manage to escape.
Sam was also raised to be a hunter like Dean and his father, but he resents the life he is forced to lead and takes the advice of a teacher who tells him to do what he wants to, not just go into the “family business”. He leaves for Stanford to study law.
Sam and his father were often at odds, arguing about everything. In many ways this is because, of the two Winchester brothers, Sam is the most like his father. Mission oriented, stubborn and locked onto a single target to the point of neglected all those around him and missing out on useful information on occasion because of this.
It's noticeable that, while Sam cares very much for his brother, his life does not revolve around his family the same way Dean's life does. This is made even more brutally obvious in the episode "Dark Side of the Moon" near the end of the 5th season.
However, despite his detachment from his family, Sam is much more capable of forming lasting relationships with people outside his family. While at Stanford Sam had a long term girlfriend, Jess, who obviously cared about and supported Sam a lot. Unfortunately for both her and Sam, Winchester's aren't allowed to be happy for long in this world and in the interest of literary symmetry (and the grand plan of Azazel of course) 22 years, to the day, after Mary Winchester died, Jess is killed in the exact same way. Sam joins Dean in a mission to hunt down the thing that killed his girlfriend, thus drawing another parallel between Sam and John.
In later seasons we find that the demon blood Sam ingested as a baby later gave him Supernatural powers, telekinesis once and various times he experiences dreams of the future. These powers are, in turn, part of the plan to create the perfect vessel for Lucifer in season 5.
Sam was named after Samuel Campbell, his and Dean's maternal grandfather, who we learn about (and find he was a hunter) in the 4th season episode "In the Beginning."
Bio by MeredithAncret