David Tennant

Benefiting from the healing undergone by his predecessor, the Tenth Doctorpossessed an outgoing, lively and genial demeanour that hid his underlying guilt, but it was still present and would appear if the Doctor was overwhelmed.

For most of his life, the Doctor was able to successfully project a convivial and even frivolous front. However, when he had to engage in conflict, the Doctor's energies would shift to reveal a fiercely protective man who resolutely guarded what he held dear, and who could be viciously unforgiving to the forces that dared menace them.

He was unique in that he was the only incarnation of the Doctor who chose to abort one of his regenerations, channelling the energy into his spare hand without changing his appearance, something his successor would attribute to suffering "vanity issues at the time".

Many of his relationships with companions were shaped, to one degree or another, by romance; he seemed to genuinely love his first companion, Rose Tyler, as the person who helped heal some of the scars of the Time War, was completely oblivious to Martha Jones' obvious affectionstoward him, and insisted upon a platonic relationship with Donna Noble. The departure of each of these companions marked periods in his life where he would abstain from having companions at all, and on one occasion he even stopped having adventures or leaving the TARDIS, with little more than a cat for company.

When travelling without companions, the weight of being the last Time Lord became much more pronounced. If prodded too much, he would erupt in an often righteous sense of fury. Indeed, the Tenth Doctor was described by the Moment as "the man who regrets". The fact that he was instantly able to recall the number of Gallifreyan children that he believed were killed at the end the war indicated just how keenly he continually felt those horrendous memories.

He met his eventual end after he absorbed a huge quantity of nuclear radiation whilst saving the life of Donna Noble's grandfather, Wilfred Mott. Delaying the process to visit all of his companions, the Doctor finally regenerated in the TARDIS, causing a huge amount of damage due to delaying the regeneration for as long as he did, and leaving his successorcrashing straight for Earth.

A day to come
This section's awfully stubby.

Info from Toil and Trouble, Scratchman & The Carrionite Curse needs to be added

The First Doctor would occasionally have premonitions of his future incarnations. (PROSE: A Big Hand for the Doctor)

The First Doctor was shown footage of the Tenth Doctor, as well as his ten other successors, by the Testimony when he expressed doubt over the Twelfth Doctor's identity. (TV: Twice Upon a Time)

When the Third Doctor answered a distress call from Harriet Jones in 2006, he found that his regeneration energy was being siphoned off into a future incarnation of himself. He also met Jackie Tyler, who told him she had seen the recently regenerated incarnation. (PROSE: The Christmas Inversion)

After their TARDISes merged with each other in the Time Vortex, the Fifth Doctor was able to remember seeing his tenth incarnation separating their TARDISes. (TV: Time Crash)

Mawdryn attempted to force the Fifth Doctor to use up his eight remaining regenerations to end his follower's cycle of perpetual rebirth, but this was rendered unnecessary when Alistair Gordon Lethbridge-Stewart made physical contact with his younger self and a discharge of temporal energy was released that allowed Mawdryn and his followers to die. (TV: Mawdryn Undead)

After losing his body to the Time Lords, the Mastermade a failed attempt to steal a regeneration from the Fifth Doctor. (PROSE: The Velvet Dark)

After the TARDIS became "stalled in the equivalent of a galactic lay-by", the Sixth Doctor had a worried thought of Peri Brown growing old and dying in the TARDIS, while he would "go on regenerating until all [his] lives [were] spent." (TV: Vengeance on Varos)

When the Master exposed the Valeyard's alliance with High Council to the Sixth Doctor at his trial, he revealed that the Valeyard was acting as the prosecutor for the trial in exchange for the Doctor's remaining regenerations. (TV: The Ultimate Foe)

When Ace was sent into the Seventh Doctor's mind, she discovered a room with thirteen cubicles, seven of them empty, while the other six contained shadowy white figures, representing the Doctor's future incarnations. (PROSE: Timewyrm: Revelation)

After sealing Gallifrey away in a pocket dimension, (TV: The Day of the Doctor) the Seventh Doctor was able to recall teaming up with his other twelve incarnations to save Gallifrey. (AUDIO: Cold Fusion)

After using a Deathworm Morphant to possess a human body, the Master tried to use the Eye of Harmony to steal the Eighth Doctor's remaining regenerations to heal himself, but his plans were foiled when Grace Holloway sent the TARDIS' into a temporal orbit. (TV: Doctor Who)

Travelling through the caves of the Death Zone to save Borusa from the Dark Tower, the War Doctor and Cinderfound various cave paintings that depicted the Doctor throughout his life; the War Doctor noticed one of "a lanky man in a blue suit", and recognised it as one of his future incarnations. (PROSE: Engines of War)

When the Ninth Doctor answered a call from Mickey Smith in 2016 San Francisco, he was told that the phone call was meant for "the other one", and quickly deduced that Mickey was talking about his next incarnation. (COMIC: The Transformed)