When the TARDIS was attacked by the Rani, The 6th Doctor was injured and forced to regenerate. After a brief period of post-regenerative confusion and amnesia (chemically induced by the Rani), the Seventh Doctor thwarted the Rani's plans, and rejoined his companion Mel for whimsical adventures in an old tower block and a Welsh holiday camo in the 1950s.
On the planet Svartos, Mel decided to leave the Doctor's company for that of intergalactic rogue Sabalom Glitz. Also at this time, the Doctor was joined by time-stranded teenager Ace. Although he did not mention it at the time, the Doctor soon recognised that an old enemy from a past adventure, the ancient entity known as Fenric, was responsible for the Time Storm which transported Ace from 1980s Perivale to Svartos in the distant future. Growing more secretive and driven from this point on, the Doctor took Ace under his wing and began teaching her about the universe, all the while keeping an eye out for Fenric's plot. The Doctor began taking a more scheming and proactive approach to defeating evil, using the Gallifreyan stellar manipulator named the Hand of Omega as part of an elaborate trap for the Daleks which resulted in the destruction of their home planet, Skaro. Soon afterwards, the Doctor used a similar tactic and another Time Lord relic to destroy a Cyberman fleet. He engineered the fall of the oppressive government of a future human colony in a single night and encountered the Gods of Ragnarok at a circus on the planet Segonax, whom he had apparently fought throughout time. Later, he was reunited with his old friend, Brigadier Lethbridge-Stewart while battling the forces of an alternate dimension on Earth.
The Seventh Doctor's manipulations were not reserved for his rivals. With the goal of helping Ace confront her past, he took her to a Victorian house in her home town of Perivale in 1883 which she had burned down in 1983. Eventually, the Doctor confronted and defeated Fenric at a British naval base during World War II, revealing Fenric's part in Ace's history. The Doctor continued to act as Ace's mentor, returning her to Perivale; however, she chose to continue travelling with him. The circumstances of her parting from the Doctor were not shown on television.
Near the end of his incarnation, the Seventh Doctor was given the responsibility of transporting the remains of his former enemy the Master from Skaro to Gallifrey. This proved to be a huge mistake; despite having a limited physical form, the Master was able to take control of the Doctor's TARDIS and cause it to land in 1999 San Francisco, where the Doctor was shot in the middle of a gang shoot-out. He was taken to a hospital, where surgeons removed the bullets but mistook the Doctor's double heartbeat forfibrillation; their attempt to save his life instead caused the Doctor to "die" with one last shocking scream. He is thus the only Doctor to have died at the (unwitting) hand of one of his own companions. Perhaps due to the anaesthesia, the Doctor did not regenerate immediately after death, unlike all previous occasions; he finally did so several hours later, while lying in the hospital's morgue.
In "Time and the Rani", the Seventh Doctor gives his age soon after his regeneration as "exactly" 953 years, indicating that some two centuries of subjective time has passed since his fourth incarnation was revealed to be 759 in "The Ribos Operation", and approximately half a century since "Revelation of the Daleks" in which the Sixth Doctorstated he was 900 years old. The later revival of the series, however, contradicts earlier episodes by establishing the Ninth Doctor as being 900 years old in "Aliens of London", with the Tenth Doctor stating his exact age as 906 in The End of Time, and the Eleventh Doctor stating his age as 909 in "The Impossible Astronaut". In "Night Terrors", the Eleventh Doctor tells an eight-year-old child that he was the same age as them "about a thousand years ago"
The Seventh Doctor has the most profound change in attitude of any of the Doctor's incarnations, beginning as someone bumbling (to the extent of putting himself in danger but not at the cost of his overall great intelligence and benevolent intentions) and progressing into a driven, dark gamemaster whose plans to defeat his adversaries, both old and new, would play out across space and time. He generally displayed an affable, curious, knowledgeable, easygoing, excitable, and charming air. However, as he began to choose his battles and keep a tighter grip on his secrets - from his plans to his very identity - he also presented more serious, contemplative, secretive, wistful, and manipulative sides with undercurrents of mischief and authority (constantly giving the impression that there was more to him than met the eye).
As something of a showman, the Doctor would sometimes act like a buffoon, usually preferring to manipulate events from behind the scenes; much like his second incarnation, he was prepared to play the fool in order to trick his foes into underestimating him, inevitably leading to their defeat at his hands. He was an adept physical performer and deployed a repertoire of magic tricks, illusions and escape artistry to this effect as part of his plans. Although his more obvious whimsical tendencies disappeared over time (particularly his spoons-playing), he maintained a fondness for idiosyncratic speeches that occasionally referred to literature, ordinary places and even food and drink amidst the weightier concerns on his mind. He was empathetic to his friends (and even his enemies, such as Helen A) and somewhat melancholic at times (such as during Mel's departure and before his decision to eradicate the Daleks) but now placed greater burdens upon himself in the name of protecting the universe. This may have led him to shroud his true intentions in mystery and the use of sleight of hand as befit his fondness for performance, in effect, subverting his more lighthearted qualities to complement and enhance his heroic and darker ones.
Given the Seventh Doctor's appearance and stature, he was surprisingly capable of both directly and indirectly taking control of situations involving strangers, using his greater intelligence to assess and direct events. Concerned with the bigger picture, he would sometimes overlook the finer details and his planning (both prepared and improvised) would sometimes have fatal results and consequences. When he acted to end threats, it was usually a ruthless, destructive and final manoeuvre. He was also not above hiding the truth from his friends and allies and using them in order to complete his schemes and gambits.
His tendency to reveal only select information to his companion Ace – as well as anyone else around them – was utilised both in her education and in their adventures, as if he were the only one who should know all the answers and others should come to their own conclusions. At two points he even abused Ace's trust in him, once to develop her as a person and again to keep her alive (on both occasions, freeing her from the evil influences that had haunted her during her life), while on one of these adventures, he showed great difficulty in admitting his foreknowledge of the situation's severity to her when she finally confronted him. In spite of his immense fondness for her, and her for him, he often frustrated her with his secretive nature as his alien behaviour, the great importance of his objectives (especially his focus on obliterating enemies from his past) and his strong desire to both educate and protect her would lead him to keep even her in the dark and would even subordinate her feelings towards him in order to succeed in their battles. Fortunately, their close, almost familial bond was likely what helped Ace in moving past the feelings of betrayal she sometimes felt towards the Doctor, particularly as he genuinely had her best interests at heart. In fact, while he appeared to be an unassuming figure, fond of performing magic tricks and displaying notable showmanship, the Seventh Doctor was actually quite powerful and calculating, for he would use his friends and foes alike as pawns in his elaborate chess game against "evil". As Ace herself put it, he was "well devious".
In direct contrast to his third incarnation, this Doctor was absolutely opposed to violence of any sort (as demonstrated in stories such as Battlefield, where he stops a battle merely by ordering the warriors to desist) and he was totally against the use of firearms (to the extent of 'talking down' a soldier ordered to execute him in The Happiness Patrol by emphasising the easiness of the kill versus the enormity of ending a life), although he also proved capable of rendering a man unconscious with a touch (Battlefield,Survival). In keeping with his established habits, he would use gadgetry of his own invention when the situation called for it, but never as his final gambit. Instead, he almost always managed to talk his enemies into submission, often into suicide – perhaps most memorably in Remembrance of the Daleks, where he taunts the seemingly last Dalekin existence until it self-destructs, or in Ghost Light, where he defeats the malevolent Light by ramming home the folly of trying to prevent evolution (he employs variations of this 'talk to death' tactic in Dragonfire, Silver Nemesis and The Curse of Fenric, although primarily to manipulate opponents to guarantee the outcome in his favour).