I saw a few posts here and on twitter about Dennis being the fourth Winchester brother, and I can't stop thinking about it.
Maybe Dennis would be born around 1998, but the brothers found out about him around 2000, because Dennis lost his mother and John took him in.
Sam would be around 15, and Dean around 19 then.
(This information would probably worsen the relationship Dean had with John, sooner as in the series.)
Dean and Sam didn't know what to do with the information, but since Dennis mother wasn't theirs and with that wasn't killed by a monster, they thought he wouldn't need to hunt.
The kid, just like Sam and Dean, spent a lot of time in motels or if it was close with Bobby. Dennis preferred to stay with Bobby and learn more about the theoretical side of the monsters than hunting them.
After Sam went to college and Dean started to hunt alone, Dennis was driving with John or staying at Bobby's. Before John vanished, he left the boy at Bobby's.
Dean then got Sam to look for John, and Dennis decided to stay at Bobby's and help them with the theoretical side and concentrate on getting into a college too.
The Winchesters killed monsters to help people, and Dennis loved helping people but maybe not fully the hunting part. So he wanted to become a doctor, and in secret specialise in people hurt by monsters.
None of the other Winchester's seemed to be mad at that decision (what made Sam a little bit jealous).
They called themselves the Winchesters trio, but most didn't know Dennis that well. (Even after finding out about Adam, mostly only Dennis recalled he had one more brother).
Dennis changed his name to Whitaker, since Dean was known as a murderer after the shapeshifter thing. It was also easier to go incognito between people who may be monsters or hunters.
Dennis became a doctor, but he never stopped being a hunter. There was always something around any hospital that wanted to hurt humans.
Of course he lived through the apocalypse after the apocalypse, ran from angels and demons, had a few tattoos to protect him and modified jewelry that became a weapon against monsters. Like the silver cross, that he specifically made into a syringe with dead man's blood.
His body was covered in scars.
He became close with Jack, they were kinda like brothers. Since both Sam and Dean were more like father figures for Dennis after John disappeared (next to Bobby), the same happened to Jack.
(so it can be said that the new god was Dennis's brother.)
Dennis religion problems, weren't particularly born from family issues, but from knowing the truth... And Chuck personally.
(In this AU Dean doesn't die, Castiel comes back and chills with the Winchester's and likes to randomly visit Dennis.)
Dennis chose the ER, because it is the closest to the adrenaline of hunting, it's different since the probability of him dying in the hospital is so much lower.
I'm thinking about Abbot being a hunter? Since he does collect dangerous hobbies.
