Riot is an Australian Shepherd who was hit by the Impala. Sam rushes the dog to a veterinary hospital and later agrees to take care of it. In another episode, Sam has memories of a Golden Retriever named Bones.

Because perceiving his actual form typically results in blindness, the angel Castiel takes a human host -- James "Jimmy" Novak, a "devout man" who agrees to become a vessel for Castiel and remains so until Heaven takes Castiel back to Heaven for "re-indoctrination" after his superiors become concerned that he is becoming too close to humans -- Dean in particular.

Harley and Sadie (aka Harley Brown and Sadie Lane) are Jared Padalecki's dogs. Rescued from the same shelter, Harley (Mastiff cross) and Sadie (German Shepherd mix) starred with Jared as part of an anti-fur campaign run by People for the Ethical treatment of Animals (PETA).

Lady Antonia Bevell is a member of the London chapter of the Men of Letters.

In "Blood Brother," the vampire Benny Lafitte says: "What I loved, it ain't here anymore. It was snuffed out long ago by monsters like me."

Crowley is a demon and the King of Hell. He was formerly the King of the Crossroads and right-hand man of the first demon and then-de facto ruler of Hell, Lilith.

After trying to lure him into a trap, Abaddon is killed by Dean with the First Blade when the Mark of Cain grants him immunity to her powers.

While tracking the First Blade, Dean and Crowley are sent to Missouri, where they find Cain tending bees on a farm.

Sam first meets Meg Masters while hitchhiking. Their first encounter is brief, as she soon gets a lift from "shady van guy."

Eventually, Cain fell in love with and married a woman named Colette. She forgave him for his past atrocities, only asking that he never kill again.