Jody Mills was the sheriff of Bobby's hometown of Sioux Falls, South Dakota. She had a son, Owen, who died and came back as a zombie during the Apocalypse. At first, she tried to prevent Sam and Dean from investigating, but when her son killed her husband, she worked with the Winchesters to kill the remaining zombies.
Amy pond is a kitsune, a werewolf-like monster that feeds on the pituitary gland, a part of the brain, without which they will die. When Sam discovers her secret, he lets her go because she saved his life. Years later, Sam notices similar killing happening again, and tracks Amy down.
Eldon Styne is the heir to the powerful Styne Family, a dynasty that causes and takes advantage of disasters such as the Nazi rise to power and the September 11th attacks to make a profit. Like all other members of his family, Eldon has received surgical enhancements including a second heart.
When Gordon Walker was 18 years old, a vampire broke into his house and abducted his sister. Gordon ran away from home, learned how to fight, hunt, and kill vampires, and tracked down the vampire who had taken his sister. He killed the vampire, as well as his sister, who had been turned, marking the beginning of his hatred for the undead.