"River Song", the primary alias of the third incarnation of Melody Pond, was a "child of the TARDIS" and the wife of the Eleventh Doctor. She was human with Time Lord characteristics, conceived by her parents, Amy Pond and Rory Williams, aboard the TARDIS as it traveled through the Time Vortex, and then raised and conditioned by the Silence. This gave her great strength, the ability to regenerate and a great understanding of the complex principles of time and space. She loved The Doctor, and shared a long-lasting relationship with him, marrying him while he was in his eleventh incarnation. River was one of the very few people who knew the Doctor's true name and, along with Clara Oswald, is one of only two companions confirmed to have met every one of the Doctor's first 13 incarnations.
Being half Time-Lord, River had the ability to regenerate and did so at least twice before she voluntarily gave up the ability to do so in order to save the Doctor's life. The Doctor's first meeting with her - from his perspective, but not from River's - ended with him witnessing her death, although a later incarnation, remembering this, would orchestrate a way for River's consciousness to be saved within a giant supercomputer.