In Season 3, Jordan Parrish becomes a Sheriff's deputy at the Beacon Hills Sheriff Station under Sheriff Noah Stilinski and is a hellhound. In Season 4, Parrish investigates a series of murders that are revealed to be assassinations. He meets Lydia Martin, then learns he is on the hit list called the Deadpool. His fellow deputy-turned-dirty Deputy Haigh attempts to kill him for his bounty by setting him on fire, but he survives. Parrish is then enlightened of the supernatural by Scott's Pack, learning he himself is supernatural and that he was drawn to Beacon Hills by the Nemeton. He helps the pack protect the remaining targets, saves Chris Argent from death and joins them in their battle against Peter Hale and Kate Argent. In Season 5, Parrish becomes close friends with Lydia, teaching her hand-to-hand combat to protect herself. During the Dread Doctors' terror spree on Beacon Hills, when the Chimeras are killed off, Parrish's hellhound alter-ego comes forward and possesses him, stealing and taking the corpses to the Nemeton, protecting the secret of the supernatural. He and the pack discover he is a hellhound, an avatar for an amortal spirit of said species, and is the prophesized enemy of the Beast of Gévaudan, resurrected by the Doctors. With Stilinski, the pack and Chris' support, Jordan eventually resolves his inner conflict and merges with his hellhound spirit, accepts his supernatural destiny and alongside the pack, vanquishes the Beast. In Season 6, Parrish investigates a series of murders with the victims pineal glands taken, then helps Scott's Pack fight against the Ghost Riders, but is enslaved to the Wild Hunt which is stuck in Beacon Hills. Parrish attempts to protect everyone from himself, but is controlled by Garrett Douglas with a ghost rider's power and used by Douglas to bend the Wild Hunt to his ends. Parrish is released from his slavery by Scott and Liam, and informs them how to save the town's people from the Hunt and foil Douglas' plans.
Jordan Parrish is an immensely resourceful, diligent and well-adjusted individual who's easy to talk to and get along with. An ex-soldier, now a sheriff's deputy, Parrish has a firm sense of duty and honor, and moral compass, dedicated to serving and protecting his community while upholding the law. Despite his age, Parrish displays great fortitude, has strong protective instincts like Sheriff Stilinski and Scott McCall and is strong-willed having shot a criminal dead in defence of a third-party victim, Brunski when he was about to murder Lydia Martin.
Parrish displays an open mind after surviving an explosion while serving in Afghanistan. He comes to grips with the idea that Lydia Martin is psychic, and when he's introduced to the supernatural world and becomes an ally of Scott's Pack, he holds himself well and willfully assists and joins their role in protecting Beacon Hills from dangerous threats. When he discovers his actions while being a hellhound, he firmly sticks to the his morals by having himself incarcerated to protect the people around him.
As a hellhound, Parrish is undeterred by what he sees as his mission to protect the supernatural world as part of the Wild Hunt, guarding the secrcy even if it means assaulting innocent bystanders.
Parrish is on the Deadpool hit list, although he has not displayed any powers as of yet. His reveal as a supernatural creature was foreshadowed in 3x23 - Insatiable when he told Sheriff Stilinski that he was drawn to Beacon Hills, using the same phrasing that Deaton used to explain what powering the nemeton would do.
Episode 4x09 - Perishable opens with Parrish tied into his cruiser. Deputy Haigh doused him with gasoline and then lights him on fire in order to collect his bounty. Somehow, Parrish doesn't die in the flames. He walks into the sheriff station covered in only soot and proceeds to beat Haigh into submission. Lydia and Scott take Jordan to see Derek, but Derek doesn't know what kind of supernatural he might be.
When Parrish goes to the sewer to save Chris, his eyes flash an orange color while they strain to bend the rebar that will release Chris from captivity.