Melody Pond

River Song, earlier a doctor and eventually a professor, was a mysterious archaeologist. She was also a convicted murderer who shared a close relationship with the Doctor. Significantly, she knew the Doctor's true name, which he would tell her at some point in his future. She would often greet him by saying "Hello, sweetie", whether in message or in person.

Although the Tenth Doctor's first meeting with her ended in her physical death, they had many adventures, from the Doctor's perspective, afterwards. Like Melanie Bush and Charley Pollard before her, she was an example of the rare companion whose timeline was not synchronous with that of the Doctor.

Biography
River Song was an archaeologist already very familiar with the Doctor when they first met, from his perspective, in the 51st century. She was, in fact, a future companion of his who would (or, from her perspective, had) travelled with him on and off. According to her, he would come to trust her implicitly, though at the start of their relationship, from his perspective, he was generally suspicious of her and occasionally almost hostile to her. Immediately prior to her encounter with the Weeping Angels, she was imprisoned in the Stormcage Containment Facility for the murder of someone she described as, "A very good man. Best man I've ever known". (DW: The Time of Angels / Flesh and Stone)

America
After receiving an invitation containing geographical co-ordinate from the Doctor, River escaped from the Stormcage Containment Facility, in order to meet him in United States of America in 2011. River met the Doctor, Amy, and Rory in a cafe in the middle of the Utah desert. The Doctor took all of them to a picnic,where they saw the Doctor murdered by someone wearing an astronaut's space suit. River, Amy, and Rory cremated the Doctors body in a 'Viking Funeral'. They returned to the cafe and discovered another Doctor, approximately two hundred years younger than the Doctor they saw die. They next travelled to the White House and then to an abandoned warehouse in Florida. River went into a maintenance tunnel in the floor. While down there, she found a nest of the Silence, but forgot about them. With Rory, she then discovered a control room to a makeshift TARDIS. (DW: The Impossible Astronaut)

Opening of the Pandorica
In the 52nd century, after receiving a phone call from Winston Churchill, River escaped from her prison to try and save the Doctor from a deadly prophecy of the TARDIS exploding. After dealing at a black market for a Time Agent vortex manipulator, River travelled back in time to the Roman era of Earth where she met the Doctor.

They proceeded to Stonehenge where they searched for the Pandorica. After located it, they discovered that Stonehenge was transmitting a signal, bringing an alliance of the Doctor's enemies to Earth. The Doctor managed to convince the assembled aliens to back away for a time, and sent River to bring the TARDIS to him. However, the TARDIS brought River to Amy's house on the 26th of June, 2010. Whe River told him the date, the Doctor realised the TARDIS was about to explode and urged River to escape. Instead, she found herself trapped as the TARDIS came under control of an unknown external force and started to explode. (DW: The Pandorica Opens)

Inside the TARDIS, River was stuck in a time loop of the first moments of the TARDIS explosion. The Doctor, using the vortex manipulator River had acquired, was able to retrieve her and bring her back to 1996. Upon joining the Doctor, River killed the Stone Dalek that was hunting them.

After the Doctor restored the universe to life, erasing himself in the process, River left her now blank TARDIS-shaped diary with Amy Pond on her wedding day in 2010 so that she could remember the Doctor back into existence. After a brief encounter with the Doctor, River teleported away with the vortex manipulator. (DW: The Big Bang)

Crash of the Byzantium
Some time after the opening of the Pandorica, River was imprisoned once again, but in an earlier century until she was put in Father Octavian's custody. If she were to carry out the mission assigned to her, she would earn her pardon. While working for Father Octavian, River was sent to be a guest on the Byzantium ship. She infiltrated the lower levels to find the Home Box, into which she carved the message "Hello Sweetie" in the Old High Gallifreyan language to attract the Doctor's attention. Leading the Doctor to Alfava Metraxis, she helped him defeat an army of Weeping Angels, who had been awakened in the planet's Maze of the Dead. (DW: The Time of Angels, Flesh and Stone)

The Library
River's expedition to the Library was financed by Felman Lux and was chartered to discover what disaster had happened there a hundred years earlier, when a cryptic final message had been sent: ">>> 4022 saved. No survivors <<<". Anticipating trouble during the expedition, River summoned the Doctor by sending him a message via psychic paper. The earlier version of the Doctor who turned up had not yet met her. Though bewildered, he agreed to help River and her team.

River and the Doctor appeared to be very close, even considering the strong bonds the Doctor forms with his companions. She still had her TARDIS-shaped diary describing her travels with the Doctor. She carried an upgraded version of the tenth incarnation's sonic screwdriver which a later Doctor had given her.

Death
As the situation in the Library deteriorated, River realised she must prove to the Doctor that she was, or would become from his viewpoint, someone he trusted completely and, with profuse apologies, she whispered his true name into his ear. The Doctor was stunned by this information, and River had won his trust. River physically died when she chose to sacrifice herself in the place of the Doctor in order to save Donna and the other 4022 people trapped in the Library's computer. She pleaded with him to not try and change history, not to change one moment of what was to come for them. After saving all the trapped people, the Doctor realized his future self must have given her his sonic screwdriver for a reason. Inside he found a data chip called a "Neural Relay", which contained River's Data Ghost. The Doctor saved her by uploading her into the virtual world contained in The Library's data core. CAL, the library's data core, controlled by a human girl (Charlotte Abigail Lux, or CAL) wired into its mainframe, also managed to save the data ghosts of all of River's dead archaeological team, in the process giving her company in the virtual world. River would go on to take care of the two virtual children and Charlotte in the virtual world, reading out her diary of her life with the Doctor and how "everybody lives" when the Doctor comes to call. Her story ended with her telling the sleeping children sweet dreams. (DW: Silence in the Library / Forest of the Dead)

The Doctor would later remember her death when Davros reminded him of the people who had died in his name. (DW: Journey's End)

Personality
River at times enjoyed showing off her knowledge in front of the Doctor, particularly knowledge of him and his personality. She would often use the word "spoilers" in reference to her knowledge of the Doctor's future, or his knowledge of her future. River was also persistent at keeping secrets from the Doctor, especially anything which could change the future. This included keeping her personal diary from him.

River showed that she cared about other people, such as the Doctor and her team in The Library, but could also be merciless, killing the Stone Dalek after it had shot the Doctor and begged for mercy when it realised who she was. She also taunted the Dalek before killing it by ordering it to beg for mercy. River Song could be cheeky, but was serious when the situation called for it.

River was also willing to sacrifice herself and took the Doctor's place when he attempted to release the people who were saved within the giant computer that controlled the Library. She pointed out that if the Doctor hooked himself up to the computer it would incinerate both his hearts and ensure that he would be unable to regenerate. In order to prevent the Doctor from killing himself, River actually knocked him out and then handcuffed him before hooking herself up to the computer. Just before her death she comforted the Doctor by saying that although it was her last meeting with him it was his first meeting with her and therefore he would see her again.

Relationship with the Doctor
River Song's relationship with the Doctor is currently a subject of mass speculation, but with each consecutive meeting so far he appears to become more trusting of her.

When the Tenth Doctor first met her she appeared to be someone he knew intimately (something she demonstrated when she stroked his hair and knew, just by his eyes, that he was much younger than "her Doctor" - hinting to some form of loving relationship) and seemed hurt when he confessed to not knowing her. Throughout the stories she made continual references to how well she knew him, even going so far as to tell the Doctor his real name to make sure she had his full trust - she described herself as someone who one day he would "trust completely" and that she herself would "trust that man to the end of the universe" (adding that they'd actually been). When she sacrificed herself to save the people in the Library (and spare the Doctor from doing it himself) the Doctor said there was only one time he could ever tell her his name (indicating that the Doctor himself, though unsure of details, did have an idea of who she is to him) to which she simply answered "shhh... spoilers" before commencing the uplink that would end her life. (DW: Silence in the Library/Forest of the Dead)

Upon the Eleventh Doctor's first meeting with her, he at first expressed resentment at the idea of his own future being set in stone but later warmed to River after her part in saving Amy (when she fixed the teleport) and after musing on the idea that "time can be rewritten." During the same episode Amy asked River if she was the Doctor's wife and when asked by River if "it could by anything that simple with the Doctor" answered "yes". River refused to confirm it, simply saying Amy was "good." Later aboard the primary flight deck of the Byzantium, when the Doctor said he "could bloody kiss [her]" River responded with "maybe when you're older" - again hinting to a romantic relationship in their future once more (and possibly ruling out the idea that she is in any way related to the Doctor as some have speculated). (DW: The Time of Angels, Flesh and Stone) By the end of the story he appeared to have at least some pleasure in anticipation of their next meeting.

Upon their second meeting the Eleventh Doctor appeared accustomed to River's style of calling him and even smiled when he saw her "graffiti" on the oldest cliff face in the universe on Planet 1. He trusted River enough to send her back to the TARDIS to bring it to the Pandorica and by the end of the two-parter they parted on good terms, with the Doctor considering the question of her identity more of a game to him, something he could wait to find out (it should also be noted that this was the second time the Doctor had the chance to read River's diary but chose not to). In the same story, when the TARDIS exploded, River Song was heard repeated saying the phrase "I'm sorry my love" - presumably to the Doctor - again hinting a romantic future relationship with the Doctor. (DW: The Pandorica Opens, The Big Bang)

Other information

 * River Song seemed to take shorter trips with the Doctor, living a more or less normal life between trips, rather than having one extended trip with the Doctor and never seeing him again after parting ways.
 * River Song was a skilled TARDIS pilot (with very different techniques from the Doctor). She mentioned that she "learned from the best," but joked that the Doctor wasn't available that day. (DW: The Time of Angels) Later she stated that the Doctor had indeed taught her. (DW: The Pandorica Opens)
 * Song appeared to have knowledge of Time Lord anatomy, including knowledge of regeneration. She indicated that destruction of both of the Doctor's hearts could be a circumstance after which regeneration was not possible. (DW: Forest of the Dead)
 * River Song had the ability to write in High Gallifreyan, but it is unknown where she learned this. (DW: The Time of Angels, The Pandorica Opens)
 * River possessed pictures of all the Doctor's incarnations (DW: The Time of Angels), though she did not know the order of the Doctor's incarnations.
 * River was sentenced to prison for murdering a man described as "a hero to many" and whom she called "A very good man. Best man I've ever known". Octavian felt that the murder victim's identity was something that the Doctor "really [didn't] want to know." (DW: Flesh and Stone)
 * Before his death, Octavian told the Doctor that "You think you know [River], but you don't. You don't understand who or what she is." (DW: Flesh and Stone)
 * River told Rory that she and the Doctor are meeting in reverse order and that every time she met him, he knew her less. She feared the day when she met a Doctor who did not know her. (DW: The Impossible Astronaut))

Behind the scenes

 * It is unknown where in time and space River Song originally came from.
 * In a recent interview by Digital Spy, Steven Moffat made a passing comment to the effect that River Song might turn out to be very different from people's presumptions as to who she really is.
 * In Doctor Who Confidential, Steven Moffat stated that we find out who River Song is in Series 6.
 * Except for flashbacks, River Song has only been used in two-part stories, all of which were written by Steven Moffat.
 * Steven Moffat dismissed the fan theory that River is a future version of Amy Pond, or that she is the Doctor's mother. (DCOM: The Time of Angels)