the TARDIS was an obsolete Type 40 TARDIS used by the Doctor as his primary means of transport. Capable, like all TARDISes, of travelling through Space and Time, the Doctor voyaged in his vessel from the Big Bang to the end of the universe in the year 100 trillion.
It was not without its share of faults. Foremost among them, it would often take the Doctor places he did not intend. The TARDIS, when it had the opportunity, claimed it took the Doctor where he wasneeded.
In his first incarnation, the Doctor implied he had built his TARDIS himself.Whether there was any truth to this or not, he and others later stated that he had, in fact, stolen it.One account claimed he had stolen the TARDIS from the Time LordMarna whilst others implied it came from the general, goverment-controlled "stockpile" of TARDISes after the model had been officially decommissioned.The Fourth Doctor told Adric that "it was in for repairs on Gallifrey when [he] borrowed it". When the Alzariancountered that he thought the Doctor outright owned the vehicle, the Doctor said, "Well, on sort of 'finders, keepers' basis, yes."
When the Doctor first decided to leave Gallifrey, he had the chance to take a Type 53, but dismissed it as "soulless" in favour of the Type 40 . The TARDIS herself said she was "a museum piece", though this may have been figurative.
None of these accounts precluded the possibility that he had somehow been responsible for its creation. Indeed, another account compromised between theft and creation. It claimed while the Doctor had not built the TARDIS from scratch, he had substantially modified/rebuilt it. According to this view he achieved control of the TARDIS without using a direct mental link. This let him bypass the feature on most TARDISes which sent a tracking signal to the Time Lords.
This notion of the Doctor bypassing a mental link with the TARDIS was muddled by other accounts that showed him having a significant mental link with the TARDIS. For instance, the TARDIS assisted him with his first regeneration and triggered a physical response in him when it was near destruction.
These accounts notwithstanding, the most direct commentary on the Doctor's acquisition of the TARDIS came from the TARDIS herself. When House transferred the soul of the TARDIS into Idris, the TARDIS gave her side of the story. She confirmed she had been out of commission, a "museum piece", when the First Doctor met her. She also confirmed that the Doctor had stolen her, denying the Eleventh Doctor's attempt to characterise the action as "borrowing". She also stated that she had stolenhim. She was unlocked and had deliberately let him steal her because she wanted to explore the and Universe sensed he would be an ideal match. According to the TARDIS, the Doctor's first words to her, some seven hundred years before, were:
You are the most beautiful thing I've ever known . . .First Doctor