Ghost

Ghosts were a phenomenon of mythology and popular culture. Those who believed in ghosts sometimes held them to be souls that could not find rest after death, and so lingered on in the world of the living. This inability to find rest was often explained as unfinished business.

A ghost was sometimes referred to as a "fetch", and the woods around Fetch Priory were long believed to be haunted, the result of its being near a Relative Continuum Displacement Zone. This anomaly leaked images and other phenomena from light years away onto Earth. (TV: Image of the Fendahl)

The quantum transducer was an extradimensional artefact that amplified residual hauntings into empathic visions. These ghosts were explained as psychic residue from powerful emotional events. The transducer was dubbed the "Ghost Machine". (TV: Ghost Machine)

Eugene Jones could interact with Gwen Cooper of Torchwood Three for a time after his death as a de facto ghost. He briefly became visible to not only Cooper, but to everyone, before "crossing over" and ceasing to be a ghost. This was due to his consumption of a Dogon Sixth Eye beforehand, granting him a new perspective on life. He would eventually unlock the secret to true peace and happiness, allowing him to let go. (TV: Random Shoes)

A Cardiff building was haunted by three cowled men with scythes. It was unknown what these things actually were, but they were considered ghosts. Toshiko Sato and Ianto Jones were sent by Torchwood Three to kill them. They appeared in front of them, and were shot dead, revealed as just "shadows" cast by the Rift. (TV: Exit Wounds)

The Mnemosyne present in the London Underground from 1903 to 2010 turned the psychic engrams of those who died in the Northern Line of the Underground into deadly, ghost-like servants with which to kill others to turn them into more servant engrams. The Mnemosyne's ghost-like engrams all perished when the Mnemosyne was destroyed. (COMIC: Ghosts of the Northern Line)

The Eleventh Doctor explained that psychic residue was a cause of many ghost sightings. (TV: The Pandorica Opens)

Sarah Jane explained that events get recorded on their surroundings and under certain circumstances can get played back again. (TV: Eye of the Gorgon)

When Sarah Jane was sent back to 1889 collect a fragment of Chronosteel, she encountered a ripple from the future, echoes of a traumatic moment that had yet to happen. Her actions helped to prevent the event from occuring. (TV: Lost in Time)

Sergeant Benton once confronted spectres, the tortured souls of his military father and child brother, who had both tragically lost their lives, holding him in contempt, to the grave and beyond. Now facing up to his traumatic past, Benton was lost in a psychotic fantasy world, a sadistic game devised by his forebearer and sibling to teach him a lesson. Finally set free, he was at last able to get back to his post where he was desperately needed. (HOMEVID: Wartime)

Professor Alistair Gryffen's numerous failed attempts to retrieve his family with the Space-Time Manipulator eventually began to take their toll on the continuum, warping reality into the shapes of his wife and children. They functioned as de facto ghosts, needing to trade places with Jorjie Turner and Darius Pike to take physical form, even going so far as to restore the Professor to his default setting, as he was before he lost them. They were ultimately banished back into nothingness. (TV: The Fall of the House of Gryffen)

The Ghostmaker and Pearl collected the last breath of humans, taking a part of their lifeforce that manifested as ghosts. (TV: From Out of the Rain)

Graham Stevens claimed that the ghost of a headless woman in white with a black dog used to walk through his bedroom at midnight. (PROSE: Cat's Cradle: Witch Mark)

In 1903, after receiving a wealth of information from the future, Grigori Rasputin saw ghosts. (AUDIO: The Wanderer)

The ghost of Harding Wellman haunted Miss Tremayne's finishing school, although the Fifth Doctor claimed that it was merely a being of pure energy who had taken on Wellman's memories and personality. (AUDIO: Winter for the Adept)

In the underwater base the Drum in 2119, a Tivolian ghost named Albar Prentis converted people into ghosts on the occasion of their death. (TV: Under the Lake) It was actually started by the Fisher King, who had originally killed Prentis in 1980. The Fisher King created the ghosts in an attempt to transmit Earth's coordinates to his race. (TV: Before the Flood)

Mistakenly identified as ghosts
The First Doctor himself was once mistaken for a ghost when an error made while he was fine-tuning the TARDIS sent him adrift through time. Between 1816 and 1890, he appeared a number of times in the restaurant of a hotel in India. The hotel's manager, Suresh Parekh, believed the Doctor to be cursing the guests as those the Doctor interacted with while he was present died shortly after. The Doctor was able to explain later, however, that it was moments in time in which a life was about to end that gave him a brief temporal stability, causing him to appear, and that he had nothing to do with the deaths. Susan eventually managed to retrieve the Doctor from the time stream. (PROSE: Indian Summer)

Sir Reginald Styles claimed that a ghost (actually a time travelling guerrilla from the future) tried to kill him. (TV: Day of the Daleks)

In 1890s London, the 51st century Magnus Greel employed the holographic technique to pretend the presence of a ghost guarding his lair under the Palace Theatre. (TV: The Talons of Weng-Chiang)

On the Moon, in 2070, Jamie McCrimmon thought a Mondasian Cyberman was a "piper phantom" of his own Scottish culture. (TV: The Moonbase) The Cybermen of Cybus Industries were once mistaken for an army of ghosts when crossing over from a parallel universe. (TV: Army of Ghosts)

The Third Doctor and Sarah Jane Smith were once mistaken for ghosts. (PROSE: The Ghosts of N-Space)

The Gelth were mistaken for ghosts, as their gaseous forms could fly and were a translucent blue, their physical forms having been destroyed during the Last Great Time War. (TV: The Unquiet Dead)

In Arcopolis, the Eyeless were mistaken for ghosts. (PROSE: The Eyeless)

The planet Arkheon was thought to be inhabited by ghosts after its destruction during the early stages of the Second Dalek War, earning it the name "Planet of Ghosts". This was in fact the Arkheon Threshold - a time rift projecting echoes onto the planet from other time periods - as explained by the Tenth Doctor, who claimed there was no such thing as ghosts. He sealed the rift after the war. (PROSE: Prisoner of the Daleks)

The "ghosts" encountered at Ashen Hill Manor were actually people who had been trapped in-between the dimensions by Erasmus Darkening's malfunctioning equipment. (TV: The Eternity Trap)

A nurse in 1918 St Teilo's Hospital thought that humans time shifting from 2008 were ghosts. (TV: To the Last Man)

The planet Kar-Charrat was rumoured to be haunted by phantoms, which turned out to be the native lifeforms' attempts to communicate with visitors. (AUDIO: The Genocide Machine)

Hila Tacorien was believed to be a ghost that haunted the Caliburn House. (TV: Hide)