Gelth

The Gelth were a humanoid species who lost their bodies in the Time War, They are villains in the Doctor Who episode called The Unquiet Dead.

Appearance
They had blue ghost-like bodies made of gas

History
They lost their bodies in the Time War againt the Daleks and tried to kill the Human race to use their bodies instead. A first Gelth inhabit and take over the dead body of Mr. Peace and kills Mr. Redpath (who is the grandson of Mr. Peace) by strangling him and then snapped his neck, Gabriel Sneel try to put the leed on her to keep her in the conflict, but she got free and went waking into the street.

The Gelth inside Mr. Peace's body was next seen at Charles Dickens' peformance, The Gelth lead Mrs. Peace's body and fly away.

They were stopped when Gwyneth sacrificed herself to close the Rift which the Gelth had used to come to Earth.