In an article posted on Entertainment Weekly's Shelf Life column, upcoming Doctor Who Series Six writer Neil Gaiman teases a very interesting hint about Idris, a character appearing in his as-yet-untitled episode scheduled to air sometime around Easter 2011. Gaiman remarked that Idris "may very well be an old acquaintance of the Doctor with a new face."
Previously, Doctor Who showrunner Steven Moffat released a tease of his own in his Production Notes column for Doctor Who Magazine #426. In a series of vague hints for Series Six, Moffat stated "The startling truth about Idris' new soul -- even the Doctor doesn't believe her!"
So presuming that this isn't some deliberate ruse designed solely to mess with hardcore Whovians, who will Idris turn out to be? According to some baby name websites, Idris is generally a male name of Welsh or Arabic origin meaning "fiery leader" or "prophet," but the Doctor Who character is presumably female due to the casting of actress Suranne Jones. With this in mind, here's my prime list of suspects:
Romanadvoratrelundar, a.k.a. Romana, a.k.a. Fred -- Last seen chronologically on television in the episode "Warriors' Gate," the Doctor's former companion Romana was written out of the series by leaving her behind in the alternate universe E-Space along with K-9 Mark II. In the Doctor Who novels written while the series was off the air between 1989 and 2005, it was revealed that Romana eventually left E-Space and returned home to Gallifrey, where she became Lady President. What happened to Romana during the Time War that destroyed Gallifrey remains unknown.
The Rani -- Last seen officially on television in the episode "Time and the Rani," the villainous Time Lady was left a prisoner of the Tetraps on the planet Tetrapyriarbus. In the Doctor Who novels, the Rani escaped the planet but ended up being killed and beheaded by a character named Father Kreiner in the novel Interference: Book One. However, her fate may have changed as a result of the Time War.
Susan Foreman (Campbell) -- Last seen in the episode "The Five Doctors," the Doctor's granddaughter and first companion was last shown returning to her home on 22nd Century Earth after being captured and brought to the Death Zone on Gallifrey by Lord President Borusa. Whether Susan survived or even participated in the events of the Time War remains unknown.
Jenny -- Last seen in the episode "The Doctor's Daughter," Jenny was a female clone artificially grown from the Doctor's genes. Although the Doctor believes her to be dead after suffering a fatal gunshot, she later returned to life but did not regenerate and was last shown traveling the universe somewhere in a stolen shuttlecraft. It should be noted that Jenny was originally slated to die in the episode, but that changed at the suggestion of none other than Steven Moffat.
Astrid Peth -- Last seen in the episode "Voyage of the Damned," Astrid was about to plunge to her death defeating Max Capricorn but dematerialized using a teleport bracelet. The Doctor used an advanced Transmat system to try to recover her, but he was only able to retrieve her in a ghost-like form so he soon allowed her atoms to scatter into space, forever travelling the cosmos. Curiously, the name Astrid (itself an anagram of TARDIS) also contains the same letters that make up the name Idris.