Meeting Rose TylerEdit
After his regeneration, he helped save London from an invasion by the Autons, living plastic automatons animated by the Nestene Consciousness. He did this with the help of Rose Tyler, a teenager whom he subsequently invited to be a companion in his travels. The Doctor showed Rose the far future and Victorian Britain (specifically Cardiff, where a space-time rift was revealed to be situated) before returning to Rose's own era, where they fought off an attempt to destroy the Earth by the alien Slitheen family. When they journeyed to Utah in 2012, the Doctor found that a single Dalek was being kept in a secret museum filled with alien artifacts. There, the first details of the Time War fought by the Time Lords and Daleks were revealed, and how it concluded with the mutual annihilation of both races, leaving the Doctor the last of the Time Lords. A young man named Adam Mitchell travelled with them from Utah.
The Doctor, Rose, and Adam travelled to the future to Satellite 5, where they discovered a plot by the Jagrafess to manipulate Earth through its mass media. When Adam tried to smuggle future knowledge back to his own time, he became the first companion to be deliberately expelled from the TARDIS. After this, Rose persuaded the Doctor to return to the day her father, Pete Tyler, died, creating a temporal paradox by saving him, which nearly led to disaster until Pete sacrificed himself to set time right once more.
Following a mysterious spaceship to wartime London in 1941, the Doctor and Rose met Captain Jack Harkness, a confidence trickster and former Time Agent from the 51st century. Jack's latest con nearly caused a deadly nanotechnological plague to sweep through the human race, but he helped the Doctor and Rose end it prior to joining the TARDIS crew.
Going back to Cardiff to refuel the TARDIS from the rift, the Doctor, Rose and Jack found that one of the Slitheen had survived, posing as Margaret Blaine, the city's mayor. Blaine was exposed to the heart of the TARDIS, and was regressed into an egg. It was during this episode that the Doctor first noticed that he and Rose had kept coming across the words "Bad Wolf".
At some point, the Ninth Doctor had at least three unchronicled adventures, involving the sinking of the RMS Titanic, the assassination of John F. Kennedy in 1963, and the eruption of Krakatoa in the 19th Century. These are revealed in "Rose", but their placement in the Ninth Doctor's chronology remains unknown. In "The Unquiet Dead", he also mentions that he "saw the Fall of Troy; World War Five [and] pushed boxes at the Boston Tea Party" but other than the first instance, when he was the First Doctor, it is unclear whether these were in his personal timeline or that of his past incarnations. He also shared an adventure with Jack and Rose in feudal Japan immediately prior to the events of the penultimate episode, "Bad Wolf".
However, the first of these adventures may actually have taken place immediately after his regeneration, since he is shown in a photo (taken in Southampton in 1912) to be wearing period clothes (Eccleston was dressed and shot specially) which resemble those worn by the Eighth Doctor. The Ninth Doctor refuses to make any concessions to contemporary fashion elsewhere in his travels (though he later insists that Rose dress appropriately for the Victorian era), being very precise about his look, which is deliberately most unlike that worn by any previous incarnations. Also, it is strongly implied that he saved the family pictured with him, by dissuading them from boarding the doomed ship — and, one episode later, he reveals that he himself was on board, and ended up clinging to an iceberg.
When the Doctor and his companions became caught in a series of deadly versions of 20th Century gameshows, they found themselves at the mercy of the Bad Wolf Corporation, based on Satellite Five, but a full century after their last visit. However, the true enemy was soon revealed to be the Daleks. The Dalek Emperor had survived the Time War, and had rebuilt the Dalek race. The Doctor sent Rose back to her own time in the TARDIS, before attempting to destroy the Dalek army. In doing so, he would have been forced to destroy a great part of the human race, which he ultimately finds himself incapable of doing. Meanwhile, after seeing more "Bad Wolf" graffiti, Rose realised it was somehow a message linking her to the events in the future.
Managing to open up the heart of the TARDIS, she absorbed the energies of the time vortex, and used it to destroy the Daleks. In order to save Rose from being consumed from within by those energies, the Doctor absorbed the fatal energy himself. However, the damage to his cells caused him to begin the regeneration process. Finally at peace with himself, his last words are, "Rose, before I go I just wanna tell you — you were fantastic...absolutely fantastic...and d'you know what? So was I!" Immediately thereafter he regenerates into 13th doctor Nicholas Lydhurst Jr