John Tull has short black hair that has receded to a widow's peak, a black full beard, and blue eyes. He wears a sleeveless brown flannel shirt and sports on his upper left arm a tattoo of a skull with flames coming out of its eye sockets.
Tull was psychotic, vicious, and ruthless; he was a notorious hitman whose M.O. was a point blank shotgun blast to the gut. His only soft spot was for his daughter, Hayley, of whom he was overprotective as suggested by the shrine he constructed of her in his trailer. It consisted of photos encased in a giant heart painted with what was presumed to be blood. There was no limit to what Tull would do to protect his daughter; he went to prison for her after he was caught disposing of her boyfriend after she stabbed him to death with a broken bottle, and mercilessly hunted down anyone who threatened her reputation or career.
It can be inferred that Tull was methodical. He planned ahead his murderous excursion in L.A. by asking to be paid in bullets, guns, and explosives for one of the jobs he carried out for the Centurian Biker Gang, which he had all intentions of using before his death. He was messy, seen by looking at his trailer, and careless since he made no effort to conceal his identity during any of his crimes, instead being ostentatious.
Hayley is Tull's daughter. He'd do anything for her, including killing anyone who threatened her reputation or career. As a desperate and last attempt he tried to kill himself and Hayley in the plane.
Upon meeting Sam, Tull took an immediate liking to her as a result of her physique. Afterwards, upon each encounter he did not hesitate to make sexual implications towards her. This paired with the fact that he killed her mentor, Bill Holton, spurred a deep hatred in Sam for Tull and an unshakeable resolve to bring him to justice, something Tull was unphased by.
John Tull is killed during the final battle on Hayley's private jet. Tull activates a grenade and attempts to kill Sam and Dave, as well as himself and Hayley, as a last resort. Samantha however shoots the airplane door and Tull is sucked out by the pressure. He is blown apart in midair as the grenade in his hand detonates before it is thrown.
- Bill Holton (Murdered)
- Gavin Routh (Murdered)
- Theresa Holland or Logan Mills (Murdered by close-range shotgun blast to the stomach)
- Jessica Greene (Attempted murder by close-range shotgun blast)
- Dave Reyes (Attempted murder through arson, strangling, and shotgun)
- Samantha Massey (Attempted murder through arson, and shotgun)
- Jamie Brooks (Attempted murder through bomb detonation)
- Rebecca McKenzie (Wounded through shotgun blast)
- Cassandra Leigh (Kidnapped)
- John Tull makes a surprise cameo appearance in Endless Summer, Book 1, Chapter 6: if Your Character entered the right password into the computer, they will create a temporal paradox and be thrown violently through other timelines and worlds, one of them being John Tull's trailer, where they narrowly avoid being shot.
- His crimes include multiple counts of murder and the kidnapping of Cassandra Leigh.
- He used to run with the Garret Clan in the Ozarks for a while.
- His appearance resembles the actor Steven Ogg who played Trevor Phillips in Grand Theft Auto 5
- He shares the same forename as John Castle, a character from the Red Carpet Diaries series.