Doc Benton

Doc Benton was a former doctor and serial killer. He needed to kill victims on a steady basis to replace his organs as his body decomposed. By doing so, he was able to continuously cheat death. He kept his formula to achieve immortality in his lab book.

Powers and Abilities

 * Immortality - His method of immortality had nothing to do with magic, only science which was apparently of his own creation. It's stated by him that there is a formula, suggesting that it was a chemical. He did however, steal other people's organs and body parts to replace his own when they ran down, or got damaged, this is most likely out of convenience though, as he can still act normally, when they are damaged beyond repair. He was also able to give others the formula, and thus his powers.
 * Super strength - Able to punch through a car window, and lift Dean up like a feather.
 * Pain resistance - Shown to not be able to feel much pain, taking several bullets in his back and chest, a knife through the heart, and punching through a glass window, all of which he took barely reacting.

Early Life
Doc Benton was once an ordinary doctor in 1816. He found the secret to becoming immortal, but years later he began to kill people to get their organs and body parts, since his kept "wearing out". A long time ago John Winchester cut his heart out using a chainsaw. This didn't kill Doc Benton though, as he was able to put himself back together and then continue his spree.

Season 3
Benton is still murdering people, so Sam and Dean go after him. Although Benton kidnaps Sam, Dean rescues him and knocks Benton out. Benton tries to convince Dean he can help him become immortal and never go to Hell. Dean thinks it over and denies his offer, not wanting to become something that isn't human. Doc Benton is last seen being buried alive by the Winchester brothers.

Seasons

 * Season 3
 * Time Is on My Side

Comics

 * Supernatural: Origins
 * Origins #4 (First appearance in terms of chronology)

Books

 * John Winchester's Journal