John Winchester
John Winchester traded his life for his oldest son's.  That's a
fact.  His sons saw to his burning funeral themselves, and
mourned the loss of their father, a brusque man, Marine to the
core, mechanic by nature, and hunter by choice.  

He was a single father after the shocking death of his wife, who
died at the hands of a demon he spent the rest of his tracking,
hunting, wanting to destroy.  He taught his sons to be hunters,
to be warriors,  instilling them with the knowledge they'd need to
continue his mission after he was gone.

Nomadic and resourceful, John Winchester had been a force to
be reckoned with.  A man one loved, hated and admired all in
one, depending on the day.  Even his friends wanted to fill him
with buckshot most of the time.
So who was this man who crawled half dead out of a
well?  A man with no memory, who would have fits
and seizures whenever he tried to remember
anything?  A man who looked hauntingly like John
Winchester, down to the injuries he'd had at his time
of death.  

If this was John Winchester, why was he back?  And
would he be able to make amends with the sons he
had left behind, Sam, who he had been estranged
from, and Dean, who never dealt with his loss well.  
Did he have a purpose to fulfill?  And could he?