1. She Was Almost Played By A Famous Hollywood Actress
When River was believed to be a one-off character, Kate Winslet was considered for the role. Once it became clear that a larger arc was planned, former ER star #AlexKingston was cast.
2. River Song First Appeared In The Two-Part Story 'Silence In The Library'/ 'Forest Of The Dead'
This makes her the second major recurring character to be introduced in a two-parter, after Jack Harkness in 'The Empty Child'/'The Doctor Dances'.
3. Alex Kingston Was Not Initially Aware That River Song Would Be A Recurring Character
She was informed of the character's full arc when filming her second appearance in the two part episode 'The Time Of Angels'/'Flesh And Stone'.
4. Early On, Some Fans Speculated That River Was A Future Incarnation Of The Doctor
She was eventually revealed as Melody Pond, the daughter of The Eleventh Doctor's companions, Amy Pond and Rory Williams.
5. She Is The Only Biological Child Of A Companion To Appear On Screen
Sarah Jane Smith's children, Luke and Sky, are adopted. Any other children have only been seen in Doctor Who Expanded Universe material.
6. River Song Is The Second Character To Possess A Vortex Manipulator
The first was Captain Jack Harkness.
7. She Is The First Woman To Marry The Doctor Onscreen, In 'The Wedding Of River Song'
While his marriage to Elizabeth The First occurred at a much earlier point in time, it was not seen until 'The Day Of The Doctor' aired two years later.
8. River Song Is A Published Author
Under the alias of Melody Malone, River wrote 'The Angel's Kiss', a novel that Amy and The Doctor are seen reading in 'The Angels Take Manhattan'.
9. She Is The Only Character To Escape The Grip Of A Weeping Angel Without Death Or Crippling Injury
River manages to get away with only a broken wrist. The Eleventh Doctor later loses a leg to a Weeping Angel.
10. She Is The Only Character Other Than The Doctor To Regenerate Onscreen More Than Once
She regenerates twice. From Melody into Mels, then from Mels into River.
11. River Is Bisexual
This was first stated by Steven Moffat in an interview, then made canon through dialogue in 'The Husbands Of River Song'.
12. Both River And The Doctor May Have Slept With Cleopatra
This is first hinted at in the episode 'The Pandorica Opens', again in 'The Wedding Of River Song', and later during an argument in 'The Husbands Of River Song'.
13. River Was The First New Series Character To Receive An Audio Series From Big Finish Productions
Two volumes of The Diary Of River Song have been released so far. River also appears in The Eighth Doctor Doom Coalition series.
14. River Song Has Appeared Alongside Six Doctors So Far.
She has shared Televised adventures with Doctors Ten, Eleven, and Twelve, and Audio adventures with Six, Seven, and Eight.
15. River Song Appears In 15 Episodes Of 'Doctor Who'
This gives her the most appearances of any non-villain recurring character in #NuWho.