A Supernatural Trinity is a trio of three supernatural beings of the three primary supernatural species - vampire, ghost and werewolf - who live with each other in harmony. This type of trinity is very rare. The most common participant in Trinities throughout the ages seemed to be Hal Yorke, who is known to have been in at least four. The name "Supernatural Trinity" originates from the name of the group which will raise the war child.
Domestic arrangements within a Trinity prove to be beneficial for all participants - ghosts are given company by beings able to perceive them, vampires are given friends to control their urges, and werewolves are given assistance during times of transformation.
- Hal Yorke, Lady Catherine and Emil Parsons - Unlike other Trinities, these three only came together on a short-term basis, intending to collaborate on a ritual to bind and slay the Devil. However, this plan failed when Hal did not use his own blood for the ritual and thus the Devil was only bound and weakened. While Hal survived, Catherine died and Emil dispersed as part of the Trinity blood ritual.
- Hal Yorke, Leo and Pearl - This Trinity lived together since Hal rescued Leo from the dogfights in 1955, and at some point afterwards were joined by Pearl. They resided together in a barbershop owned by Leo, until 2012, when Leo became too old and weak to survive further transformations. Leo died, and passed over with Pearl in 2012, and Hal relocated to living with Tom and Annie.
- John Mitchell, George Sands and Annie Sawyer - A Trinity which started when Mitchell saved George from an attack by vampires, and the two subsequently became friends and moved into Annie Sawyer's home, where they met and befriended Annie's ghost. This Trinity eventually expanded to include George's girlfriend Nina Pickering, after she became a werewolf due to George scratching her during a transformation. Mitchell was staked by George as a mercy killing after he gave into his instincts, Nina was assaulted and killed by vampires, and George died after forcing a partial transformation without the full moon as his body couldn't cope with the physical stress.
- Adam Jacobs, Christa Stammers and Matt Bolton - A short-lived Trinity which formed when Adam met Christa then later Matt at school, and the trio decided to investigate Matt's death together. Adam apparently left this Trinity at some point, and Christa eventually killed two people in her werewolf state, running away afterwards. Matt's status is unknown.
- Hal Yorke, Thomas McNair and Annie Sawyer - A Trinity which formed after Tom moved in with Annie Sawyer and Eve Sands as George's dying wish, and when Hal later came to stay with Tom and Annie following Leo and Pearl's departure. This Trinity was also correctly prophesied in the Skin Parchments as the one which the War Child would come from the house of. Annie and Eve crossed over after fulfilling the War Child prophecy.
- Hal Yorke, Thomas McNair and Alex Millar - This Trinity formed shortly after Annie and Eve's passing over, when the recently-deceased Alex was forced to stay with Tom and Hal until she could pass over. This Trinity were responsible first for restoring the Devil to power, then for confronting and trying to kill him before he could start the Apocalypse. They are currently trapped by Hatch in a dream reality where they believed they'd defeated him and become human. This trinity is considered to be the polar opposites of the Mitchell, George and Annie trinity in terms of personality.
- Aidan Waite, Josh Levison and Sally Malik - This is the only known Trinity in the American remake of Being Human shown on the Syfy channel. This Trinity was created after Aidan saved Josh from a group of vampires and when they moved into the house Sally was haunting. It later expanded to include Nora Sergeant after she became a werewolf because of Josh scratching her. This Trinity ended when Sally resurrected Aidan as a human, disappearing as a result and ending on the other side. Later Aidan himself was killed from a fire, coming back as a ghost before going through his door. Josh and Nora are left to continue a "normal" life as werewolf parents. In an alternate timeline, this Trinity never truly came to be due to Sally preventing her death, being human while living with Aidan and Josh. When she died again, Aidan had joined the vampires and his relationship with Josh was destroyed. However, in the end the three worked together to correct the timeline.
- John Mitchell, George Sands and Annie Sawyer - This Trinity was only seen in the original pilot episode of the UK series. While Mitchell and Annie share their name with their canon counterparts, they are different people entirely, along with a number of other people in their lives. While it is unknown how Mitchell and George met, though it was presumably similar to their canon counterparts, the Trinity was complete when they moved into Annie's house. This group was last seen hanging out after Annie conquered her fear of leaving the house and George's ex learning of his condition, while Mitchell is warned by Herrick that he has big plans along with Lauren.
Power against the Devil
The Supernatural Trinity in the BBC universe is capable of weakening and even destroying the Devil, through a blood ritual which uses the Trinity's power against the Devil. The ritual involves the Trinity first summoning the Devil to their location and then allowing him to possess a human vessel. The ghost member of the Trinity will then drink blood from the vampire and werewolf of the Trinity to complete the ritual.
If the ritual is carried out properly, then the Devil, while able to leave his vessel, will be trapped at and unable to flee the current location, and will be made destroyable while in a human vessel. However, if the ritual is improper due to it not being a true Trinity (for example, if the blood of a vampire who doesn't form the werewolf and ghost participants' trinity is used), then the Devil will instead just be weakened and bound within his current vessel, barely able to feed or to extend his power, until he can replenish himself.
A consequence of the blood ritual is that once it is performed, the vampire and werewolf members will begin to die seemingly by choking, and the ghost will begin to disperse. The dream world that Hatch trapped Hal, Tom and Alex in depicted that if the trinity ritual was successfully carried out and used to kill the Devil, then the Trinity responsible would survive and would be reverted to their human states by the Devil's destruction, while other supernatural creatures will become human, thought this is only known to have happened to werewolves; although due to the illusion's purpose, it is unknown whether or not this would happen if the Devil was successfully slain with the ritual in reality.
Because the Devil never appeared in the American remake, but is mentioned to be called Lucifer, it is unknown if the Trinity has any power over him. It is also unknown if he exists in the reality of the original BBC pilot.