The Winchesters and Adam

Sam, Dean and Adam are brothers. Adam is their half brother John kept kept away from the hunting lifestyle. So unlike Sam and Dean, Adam is not a hunter. Unfortunally, Adam is killed before they really meet him.

Background
Adam was born September 29, 1990 to his mother Kate Milligan. When he was 12, he begged his mother to call John. When John heard he had a son, he dropped everything (Sam and Dean remember that and didn't know what happened til they met Adam). He was an Eagle Scout, graduated from high school with honors, and attended the University of Wisconsin, where he majored in biology and was pre-med. Then a week before Jump the Shark, Adam is eaten and killed by a ghoul. The ghoul now impressionating Adam calls John, but gets Sam and Dean instead.

Season 4
(For now we're going to refer to the ghoul being Adam, as Adam. When its revealed that "Adam" is not Adam, there will be quotation marks). "This thing killed my mom. If you're hunting it, I want in."

- Adam Sam and Dean are very surprised to hear they have a half brother. Dean, is very suspicious, and thinks it to be a trap. So they head to a diner to meet him. Dean steps up the area in case this "Adam" is a shapeshifter, or demon.

Season 5
"Adam, you may not believe it, but Dad was trying to protect you, keeping you from all this. Yeah, well I guess the monster that ate me didn't get that memo."

- Dean and Adam