River Song is a fictional character from the British television series Doctor Who. She is portrayed by actress Alex Kingston and is known for her complex relationship with the Doctor, a time-traveling alien Time Lord. River is introduced as a mysterious figure with a deep connection to the Doctor, often revealing her knowledge of his future while he learns about her past. River Song first appears in the episode "Silence in the Library," where she meets the Tenth Doctor, played by David Tennant. Throughout the series, her character evolves, showcasing her adventurous spirit and expertise in archaeology. River's storyline intertwines with key events in the Doctor's life, making her a significant figure in the show's narrative.