River Song Is Another Time-Traveller and Will, or To River Been a Close Freind. But everytime the doctor sees River, River knows his future and the Doctor knows her past as they are both Time-Travellers and meet up at the wrong order

Big bang 2

River In the Series 6 Two-Parter Finale, 'The Pandorica Opens' and 'The Big Bang'

She always has a clever trick up her sleave and always has an escape route or plan. She carries a pistol and a yet unidentified sonic item she uses in 'The Impossible Astronaut, Series 6, Episode 1'

We Saw Her Untimely Death With the Tenth Doctor In The Two-Parter 'Silence in The Libary' and 'Forest of The Dead' when she died all to save her dear doctor, these are the 'Worst Days To Come' as she says in the new Series with young doctor, Matthew Smith.

Nobody Knows much about Her, not even The Doctor, Amy, Rory, Or Even Canton