Time And Relative Dimension In Space, more commonly known as The TARDIS, called Sexy by The Doctor when he is alone with her, is the Time and Space Machine used by the Doctor in the British Sci-Fi Show, Doctor Who. It was thought to have been non-living in the early days of Doctor Who, but after a few seasons, it was suggest that it was alive. About the same time, it was suggested, likely as a reference to Sailors and their ships, that she was female.
The TARDIS's origins are unknown. However, it is known that before the Doctor arrived, she had two owners:
Marianna: The first known owner of the TARDIS. She was a Time Lady that got trapped inside the TARDIS looking for the Point of Stillness.
Marnel: He was the owner prior to the Doctor. His TARDIS was supposedly stolen by the Doctor's supposed parents, Ulysses and Penelope. He was supposedly stuck on Earth with Mrs. Gate, Penelope's mother. Ulysses and Penelope supposedly broke the TARDIS and landed it in a repair station, just below Gallifrey City on Gallifrey.
At the repair station, the Doctor, in his first incarnation, and his granddaughter, Susan Foreman, were planning to steal a Type 53 TARDIS, but a form of Clara Oswald, who in the Doctor's future, jumped into the Doctor's Timeline to stop the Great Intelligence, who also jumped into the Doctor's timeline, from destroying the Doctor. She told him to take the Type 40 TARDIS, as the Doctor would have more fun using the Type 40. The Doctor did so and when he entered, he said that the TARDIS was "the Most beautiful thing I [he] have [had] ever known".
Since then, he has spent his life using the TARDIS as his main base/home, with the exception of 1970-1973, when he was exiled to Earth, and the at least 800 years that he remained on Christmas, Trenzalore.
The TARDIS was once put into the body of a Time Lady named, "Idris". In this form, she and the Doctor got to speak for the day. She helped him stop House, a sentient trash planet that took control of the TARDIS shell and trapped Amy and Rory. At the end of the day, her body was wearing down. Using her last words, she said hello to the Doctor as she never got to as the TARDIS.