Gelth The Gelth were a humanoid species who lost their bodies in the Time War . Biology . Though the Gelth originally had biological bodies , they were eventually reduced to a gaseous form during the Time War , after their bodies were destroyed during the conflict . They could shape this gas into a wraith - like form , but they needed to be in a gaseous environment to survive . Once there , the Gelth emitted ghostly screams as they floated around the location at which they congregated . The Gelth could take control of human corpses , though only with difficulty . While inhabiting the corpses , the Gelth could control and move the dead humans as walking zombie s , leaking glowing blue gas that streamed through the mouth . While controlling a human , they tended to continue unfinished business . The Gelth would eventually be forced out of the corpse over time or if there was a lot of gas in the air around them . ( TV : " The Unquiet Dead " ) History . During the Last Great Time War , billions of Gelth were turned into gas . Eventually , they discovered the Rift , which opened into Gabriel Sneed ' s mortuary in 1869 . They were attracted to the area , since they could inhabit the gas found in the pipes and emerge through gas lamps . They also discovered that they could survive in the gases in a decomposing human and , as the Ninth Doctor put it , " use it as a vehicle " . The Gelth contacted Gwyneth , Sneed ' s servant , who had psychic ability . She thought of the Gelth as angels . Through Gwyneth , the Gelth spoke with the Doctor . Presenting themselves as peaceful and facing extinction , the Gelth asked for the Doctor ' s help in allowing Gwyneth to open the time rift further , allowing through more of their kind . The suggestion of doing this and allowing more Gelth through the rift to inhabit the corpses of humans was an idea which horrified the Doctor ' s companion , Rose . The Doctor , however , accepted the idea as an interim stage before taking the Gelth to a place where he could help them acquire new , specially - created bodies . With the rift opened wider , the Gelth , however , planned to let all the billions of Gelth through and take the planet by force . Gwyneth closed the rift in time , however , and destroyed the remaining Gelth with fire . ( TV : " The Unquiet Dead " ) When travelling alone , the Tenth Doctor encountered a small group of Gelth in the crypt of Cheltnam Abbey who bridged a gap in the Rift through Preston Gilchrist while on the TV show " Scared Stiff " . The Gelth possessed the bodies of several skeleton s from the crypt of the abbey , along with Preston , as they attempted to open the Rift permanently . The Doctor distracted Preston by revealing that the television show was a fake , thereby giving him time to close the Rift and trap the Gelth . ( PROSE : " Scared Stiff " ) Other references . Rose Tyler noted the Gelth among the things she had seen when she was sceptical that the newly regenerated Tenth Doctor was the man she knew . ( TV : " Children in Need Special " ) While attempting to bluff the Sycorax into leaving Earth alone , Rose tried to invoke the authority of the " Gelth Confederacy " , among other species she had encountered on her travels . ( TV : " The Christmas Invasion " ) Rose also suspected the Gelth for the appearances of ghost s across the world , this was later revealed to be the Cybermen from a parallel Earth preparing an invasion . ( TV : " Army of Ghosts " ) The Gelth were one of the explanations the Doctor gave on Arcopolis for ghosts . ( PROSE : " The Eyeless " ) Behind the scenes . According to " The Brilliant Book 2012 " , a book that contains non - narrative based information this wiki doesn ' t consider a valid source , in the timeline created by River Song refusing to kill the Doctor , the Gelth tried to contact Charles Dickens via social networking websites . Dickens told them he wasn ' t " falling for that one again " and blocked them .