River (aka Melody Pond), mostly played by Alex Kingston, is the daughter of Amy Pond (Karen Gillan) and her husband Rory (Arthur Darvill) - as well as being the Doctor's wife.
She's appeared across various eras of Doctor Who, meeting numerous iterations of the Doctor - and confusing and enchanting the Time Lord all the while.
It's not long into their relationship that we discover the pair are meeting all out of order, and that River knows a lot about the Doctor - including his name.
Thankfully, River has her diary to keep track of - but for viewers, it can get a little confusing.
So, at what point did River first actually meet the Doctor? Read on for everything you need to know about River Song and her timeline! No spoilers, we promise...
River Song's timeline in Doctor Who
River Song's birth - A Good Man Goes to War (season 6, episode 7)
River's true identity isn't revealed until season 6 episode 7, when we learn about the story of her birth.
The Eleventh Doctor (Matt Smith) is on a mission to rescue Amy after she's been kidnapped following the birth of her daughter Melody on Demon's Run.
It's revealed, in a very awkward chat between the Doctor and Amy, that River is a child of the TARDIS, meaning she was conceived while the TARDIS was in flight - and that she can regenerate.
River reveals who she is to the Doctor in this episode later in her timeline but, while she's a baby, she's kidnapped by the Silence.
River Song's first regeneration - The Impossible Astronaut/The Day of the Moon (season 6, episodes 1 and 2)
The dramatic two-parter, which sees the Doctor "die" at the hands of River, is full of different variations of the pair of them.
However, River is also shown as a young child (played by Sydney Wade), who can only be kept alive in a spacesuit - and who Amy shoots (not knowing she's her daughter).
The ending to the story shows a young River telling a passer-by that she's dying but reassures him that she knows how to "fix it", before regenerating.
Let's Kill Hitler (season 6, episode 8)
After she regenerates, River/Melody goes by the name of Mels (played by Nina Toussaint-White) and grows up as the best friend of her parents, Amy and Rory.
To make things even more confusing, she even plays a part in getting her parents to realise their feelings for each other.
The episode also features River's second regeneration, into the form we know her best as (played by Alex Kingston).
Closing Time (season 6, episode 12)
It's tragically revealed in Closing Time that River has not been able to escape the Silence.
Madame Kovarian (Frances Barber) informs her that she will be the one to kill the Doctor, and she's forced into the space suit to carry out the horrifying task - although, thankfully, things pan out a little differently.
The Wedding of River Song (season 6, episode 13)
After River refuses to kill the Doctor, time starts to disintegrate.
River marries the Doctor and, despite her refusal, he urges her to "kill" him, setting time straight again.
However, he reveals to River that he managed to escape his own death using the shape-shifting Teselecta. Rule one - the Doctor lies!
A Good Man Goes to War and The Impossible Astronaut/The Day of the Moon - again (season 6, episodes 7, 1 and 2)
Here, we've got to go backwards to go forwards. Stay with us!
River is imprisoned in the Stormcage for killing the Doctor (sort of) but breaks out to reveal who she is to her parents, Amy and Rory, in A Good Man Goes to War, showing them their daughter's name in the language of the forest - River.
She then receives her invitation to the beach for the events in The Impossible Astronaut and watches the other version of herself "kill" the Doctor.
A younger version of the Doctor, who also received an invitation, meets up with the gang, and they travel to 1969 to take on the Silence once and for all - River with an impressive gun, and the Doctor with his sonic screwdriver.
The Pandorica Opens/The Big Bang (season 5, episodes 12 and 13)
River, being River, leaves a flirty message for the Doctor on a diamond cliff, ensuring it's the first recorded message in history.
Following the message, the Doctor meets up with River and she shows him a painting of the TARDIS exploding.
They go to Stonehenge to uncover the Pandorica and the Doctor urges River to bring the TARDIS. The TARDIS starts to explode with River still inside, before the Doctor is sealed in the Pandorica.
The Doctor manages to save River, who is kept alive in the TARDIS by a time loop, and creates a second big bang to all but reboot the universe.
Amy and Rory celebrate their wedding day which River, being River, attends (although she technically hasn't been born yet).
The Time of Angels (season 5, episode 4)
The Time of Angels was only the second time the Doctor met River in his timeline, but it was one of the final stages in hers.
The Doctor meets River at the crash of the Byzantium and we see an epic return for the Weeping Angels.
While Amy is almost trapped, the Doctor defeats the Angels by detonating the gravity globe he'd placed there earlier.
The Wedding of River Song - again (season 6, episode 13)
River then goes to visit her parents, Amy and Rory, while they believe that the Doctor is dead. She informs them that he's alive and tells them about his plan.
The Angels Take Manhattan (season 7, episode 5)
In one of the most heartbreaking episodes in the history of Doctor Who, the Weeping Angels return and this time, not everyone makes it out.
The Doctor, River, Amy and Rory battle the Angels, but Rory is transported back in time. Amy sacrifices herself to be with him and River is forced to watch her parents disappear - but she sees their names together on their graves and knows Amy managed to find Rory.
More like this
The Husbands of River Song (2015 Christmas special)
As part of the 2015 Christmas special, River meets the Twelfth Doctor (Peter Capaldi) for the first time and doesn't recognise him due to his regeneration.
During their adventure together, River realises they're headed for the planet Darillium, which the Doctor knows is their last night together before her death. He gives her a Sonic Screwdriver, preparing for their meeting in Silence in the Library.
Silence in the Library/Forest of the Dead (season 4, episodes 8 and 9)
Silence in the Library was River's first appearance in Doctor Who and the first time the Doctor met her but, due to their timelines being out of order, it would be the last time she saw him (kind of).
River sacrifices herself in place of the Doctor (David Tennant), hooking herself to the computer terminal to defeat the Vashta Nerada.
However, she doesn't exactly die and is saved as a digital ghost along with the rest of the Vashta Nerada's victims.
The Name of the Doctor (season 7, episode 13)
Appearing for one final time, River is able to make a brief escape and say goodbye to the Doctor.