Trinity Killer

Arthur Mitchell
Dexter character
John Lithgow as Arthur Mitchell
First appearance	"Living the Dream"
Last appearance	"The Getaway"
Portrayed by	John Lithgow
Information
Occupation	Teacher Deacon Charity entrepreneur
Family	Vera Mitchell (sister, deceased) Henry Mitchell (father, deceased) Marsha Mitchell (mother, deceased)
Spouse(s)	Sally Mitchell (wife, deceased)
Children	Jonah Mitchell (son) Rebecca Mitchell (daughter, deceased) Christine Hill (daughter, deceased)

Arthur Mitchell, often referred to as the "Trinity Killer", is a fictional character in the Showtime TV series Dexter. The character is portrayed by John Lithgow, who won a Golden Globe Award and a Primetime Emmy Award for his performance. He is the main antagonist in season four. In 2016, Rolling Stone ranked him #34 of their "40 Greatest TV Villains of All Time".

Arthur Mitchell is an unassuming suburbanite and family man — who for 30 years has been living a double life as a serial killer. FBI agent Frank Lundy dubs him the "Trinity Killer" because of a recurring pattern of three killings. First, Mitchell would kill a young woman in a bathtub by slicing her femoral artery with a straight razor while putting her in a choke hold, and holding up a small mirror so that he can see her face as she dies. His second victim is a married mother of two, whom he kidnaps and forces to jump to her death from an abandoned building. His third victim is a father of two, whom he bludgeons to death with a hammer. At each site he places a small sample of his sister's ashes, and arranges the victim's arm to point at the ash. He has repeated this cycle in different cities all over the United States. Frank Lundy's superiors are skeptical about the existence of the Trinity Killer, leading him to launch a private inquiry into the murders that eluded him during his FBI career.

It is later discovered that, before these three, the Trinity Killer also kidnaps a young boy whom he dresses in cowboy pajamas and convinces to play with a train set in a recreation of his childhood. Following this, he will bury the boy alive in cement at a Four Walls' building site. These killings were not connected to the pattern until shortly before Mitchell's death, because the boys were reported as missing rather than dead.

At first, Dexter Morgan is fascinated by Mitchell's efficient killing methods and apparent ability to balance his familial responsibilities with his secret life as a serial killer.