Peter Hale is Derek's uncle, a hereditary werewolf, the main antagonist of Season 1, one of the main antagonists of Season 4, and a major antagonist of the entire series. In the Hale Fire, Peter was badly burned, rendered comatose for six years. In the episode "Wolf's Bane", Peter is revealed to be the Alpha werewolf who killed Derek's sister Laura, his niece, to become an Alpha, Bitten Scott McCall and committed the murders throughout Season 1. Peter is sociopathic, manipulative, smart with his actions, sarcastic and power-hungry willing to do anything in his pursuit of power. The people he killed were arsonists and conspirators involved in the Hale Fire. Later on in "Formality", Peter attacks and Bites Lydia and in "Code Breaker", the Season 1 finale, Peter kills Kate Argent, the final culprit in the conspiracy. Peter is defeated by being burned alive by Scott, Allison, Stiles, and Jackson. Derek then kills Peter to become the new Alpha.
In Season 2, Peter appears in Lydia's hallucinations as a teenager, successfully seducing Lydia before revealing his true identity, to her horror. Peter knew Lydia would be immune to the Bite, so instead Peter had spiritually imprinted himself in Lydia as his back-up plan, should he be killed. He psychologically tortures Lydia into following his instructions. In "Party Guessed" by using Derek's blood as an Alpha and the light of the Worm Moon, Peter successfully has Lydia resurrect him. It is revealed by Deaton, that Peter lost his Alpha status upon resurrection and his abilities are subsequently impaired.[7] Throughout Season 3, Peter has an uneasy alliance with Derek and the gang after helping them against the Kanima. It's depicted in the past that even before the fire, Peter was a manipulator and a trouble maker; he started a chain of events that lead to the death of Derek's first love, Paige. Peter felt envy and resentment over his older sister Talia's leadership of their family, firmly believing the role of Alpha was his. Sneaky and malicious as always, Peter has shown to somewhat care about his remaining family, Derek and his other niece Cora, most likely out of convenience. When Cora is dying of mistletoe poisoning in "Alpha Pact", Peter tells Derek of a technique to cure sickness with pain transference as a way to save her, but he'll give up his Alpha status. When Derek decides to go through with it, Peter sneakily grins in triumph. In the mid-Season finale, after Scott becomes a True Alpha, Peter prevents Jennifer from attempting to re-energize herself using the Nemeton again. The Darach reveals she knows he plans to kill Scott to become an Alpha agin. Peter kills Jennifer, proudly and malevolently boasting that he's "always been the Alpha". In Season 3B, Peter goes along with Derek on the latter's mission to recover Talia's claws from the Calaveras. Derek has Peter use Talia's claws to conduct a ritual so Derek could communicate with Talia, in exchange he tells his nephew he wants to keep the claws. In "Letharia Vulpina", Peter tells Lydia he will help her control her banshee nature on the condition that she do something for him: he wants her to listen to Talia's claws and translate a memory that she had wiped from him before her death. Lydia manages to listen and she discovers that Peter had fathered a child, the werecoyote Malia Tate, but refrains from telling him her name. In "De-Void", after the Pack paralyze Void Stiles' body, Lydia calls Peter for help. He complies, but Lydia has to give him his child's name. Peter shows Scott how to utilize an Alpha's power to meld minds so that he and Lydia can enter Stiles' mind to find Stiles and guide him back. Lydia gives Peter Malia's name.

In episode "117" of Season 4, Peter comes face-to-face with Malia, to his shock, though Malia is initially kept in the dark about her relation to him. Peter has also regained his full strength and werewolf abilities. He learns of Kate Argent's survival and faces off against her when she infiltrates the Hale vault, but 'the Benefactor' simultaneously robs the Hales' fortune, $117 million in bearer bonds, to his anger. In "Orphaned", Peter approaches Kate with a proposition: he offers her control over her werejaguar shapeshift. In return, she helps him recover his money and implement his plan to kill Scott. In "Time of Death", Peter meets with Malia after she finds out he's her biological father, showing her the file confirming her adoption. He offers her his help in finding her biological mother whom is known as 'the Desert Wolf'. After it's revealed Meredith Walker is the Benefactor in "Monstruous", Peter, reading Meredith's mind, sees that through Meredith telepathically hearing his vengeful thoughts, he was responsible for the Dead Pool. He is amused by the whole ordeal, defending himself saying his 'plan' was the ravings of a lunatic, that comatose for a werewolf is beyond torture. At the end of Season 4, Peter and Kate initiate the plan to kill Scott. Kate abducts Scott and transforms him into a Berserker. Peter goes along with the Pack when they rally to go up against Kate, ostensibly promising Malia she'll meet her mother if she kills Kate, and imploring the Pack not to hold back against the Berserkers. The plan fails at the last minute when Scott is able to break free of being a Berserker. Scott confronts Peter that he figured the plan out to kill him for power. Showing his true colors, Peter viciously retorts that he pursues power for his family, that the one to inherit it is him, telling his werewolf progeny he doesn't deserve his power. Peter clashes against Scott. Peter gets the upper hand but Scott triggers new strength and swiftly defeats Peter, telling him he "was never an Alpha, he was always a monster". Peter is drugged with yellow monkshood, brought back to Beacon Hills, and incarcerated in the supernatural ward of Eichen House. He is temporarily held in a cell with Valack before being moved to his own cell.