Samuel "Sam" Winchester is a hunter, along with his older brother Dean. He is one of the main protagonists of Supernatural. It has been argued that he is the smarter of the Winchester brothers, although Sam himself would disagree.

Over time Sam has accepted the Hunting lifestyle and has repeatedly sacrificed himself for the greater good, highlighting his selfless nature.

The Winchester brothers hunt down mystical creatures and urban legends like the folklore's Bloody Mary, and Shapeshifters. Generally, each episode revolves around a relatively uniform structure: the brothers find a case and solve it.

Although Sam's brother, Dean, has been mainly responsible for gathering hunting leads at this point, Sam's episodes of precognition and telekinesis soon direct them to where several of their hunts take place.

Sam is a senior at Stanford University who is applying for law school. Sam also has a girlfriend, Jessica Moore, whom he lives with and is secretly planning to marry. One night, Dean comes to Sam's apartment to seek his help after their father goes missing; although reluctant at first, Sam eventually accompanies his brother.

(Source: Supernatural Wikia)