Companion (Doctor Who) "Face the Raven", but in a subsequent episode ("Hell Bent") her time stream is frozen at the moment of death by the Time Lords so that they can interrogate her about the Hybrid; the Doctor takes advantage of this to save her life, but she remains technically neither alive nor dead, does not age or have a pulse. After her departure as a companion of the Twelfth Doctor, she teams with the immortal Ashildr and travels in a stolen TARDIS. Other companions died in alternate timelines or alternate lives. "Brigade Leader" Alistair Lethbridge-Stewart, "Section Leader" Liz Shaw, and "Platoon Leader"
Companion (Doctor Who) was written out by the unusual method within the series of being "killed off". By the time of the Sixth Doctor, a single companion had become standard again. Although the term "companion" is designated to specific characters by the show's producers and appears in the BBC's promotional material and off-screen fictional terminology, there is no formal definition that constitutes such a designation. The definition of who is and is not a companion becomes less clear in the newer series. For instance, Stephen Brook in "The Guardian" newspaper's Organgrinder blog discounted Michelle Ryan as a likely next companion but said that