Even with Supernatural being a dark fantasy series, the show placed heavy emphasis on character quality. Dean Winchester was one of the two leads alongside his brother Sam, although Dean had arguably the more tragic arc. This was due to Dean's selfless love for his brother that saw him sacrifice his own life and happiness to ensure that Sam remained safe.
A look at Dean Winchester's timeline gives the best view into how tragic his life was, along with the events that led to the conclusion of his arc. Since the Supernatural timeline is told out of order due to Dean's experiences with time travel, his story takes shape before he was even born.
1861: Dean Retrieves Phoenix Ashes From The Old West
1943: Dean Retrieves The Hand Of God From The Doomed USS 'Bluefin'
1944: Dean Teams Up With Eliot Ness
1973: Dean Meets His Parents, John Winchester & Mary Campbell
1978: Dean & Sam Stop The Angel Anna From Slaying John & Mary