Legacy Character Study: The 5th Doctor

So. How do you follow up the most popular lead evar on a popular TV show?

Apparently, like this.

Character Conception
The casting of Peter Davison was different than the other casting up to that point, thanks to Tom Baker. Baker had a ridiculously popular and ridiculously long run as the Doctor, so they decided to cast an already-popular actor to replace him, in the hopes that the change would be more accepted. Davison already had critical acclaim in his role in All Creatures Great and Small. To compare, it would be like... I don't know, putting the Reading Rainbow guy in Star Trek.

Wait a minute....

Davison, at the age of 26 was the youngest Doctor in the show's history until the casting of Matt Smith. As such, this new, young Doctor was written in a surprisingly different way than previous Doctors.

Secret Origin
The Doctor foiled the Master's... um, master plan for the ransom of the universe, but sacrificed his life in the process. 5's regeneration was less than smooth sailing, giving him temporary amnesia as well as requiring him to rest at a place called Castrovalva. 
...which would turn out to be a mental construction of the Master's. 

After refoiling the Master's scheme, the Doctor flew the TARDIS back into time and space.

Powers/Abilities 
This Doctor demonstrated a heightened sense of taste. Not taste as in "dress sense," what with the fact that he wore celery.

I wear celery now.  Celery is cool.

You might think that's a weird thing to bring up. You'd be right, but bear with me. It was revealed at the end of 5's run that he was allergic to "certain gasses in the praxis range," whatever that means. If he encountered any, the gas would turn his celery purple. Then he'd eat the celery to counteract his allergy. Weird.

The 5th Doctor also exhibited the ability to survive in a vacuum, if only for a bit. Speaking of the lack of breathable air, 5 was also able to use his advanced Gallifreyan lungs to hold his breath for several minutes at a time.

Companions 
Adric 
Adric developed the unfortunate habit of pretending to side with the villains, leading to the audience (semi-jokingly) thinking of him as a traitor. Adric would demonstrate his undying (no pun intended) loyalty to the Doctor when he ended up giving his life to foil the Cybermen's latest plan to take over Earth.

Nyssa 
Nyssa left the TARDIS to help the inhabitants of space station Terminus fight Lazar's Disease.

Tegan 
After accidentally being left behind at Heathrow, Tegan rejoined with the Doctor, only to later leave again; she was unable to handle the beginnings of the latest Dalek civil war.

Turlough 
Vislor Turlough, an alien hiding on Earth as a schoolboy who came under the influence of the Black Guardian. After regaining his independence, he traveled up with the Doctor until leaving when he discover his younger brother was still alive. Possibly the most enigmatic companion, Turlough was quick to defend himself, and actually rather selfish. But like most companions, the Doctor's compassion rubbed off on him.

Kamelion 
Originally a villain, the robotic shapeshifter Kamelion joined up with the Doctor, only to disappear until a few episodes later, where Kamelion died. Behind the scenes, the guy who coded for the robot's animatronics had passed away, so they were left with a prop that they couldn't use after its first appearance.

Peri 
Perpugilliam "Peri" Brown became the latest in a long line of long-named female companions; she was one of the longest-lasting companions in the show's history. She was an American botany student that the Doctor met after Turlough saved her from drowning and the evil Kamelion posed as her dead stepfather. She didn't like Turlough that much, due to his past as a villain. Peri is best remembered for the unique assets she brought to the show. 

Both of them.

Okay, obligatory joke out of the way, Peri was a very basic companion, in that she fulfilled the basic roles of need stuff explained and needing to be rescued. But the actress also brought a general warmness and down-to-earthiness that the Doctor would often lack, due to his alien nature.

Notable Enemies 
The Black Guardian 
The Black Guardian, vowing revenge on the Doctor, returned with new minions Kamelion and Turlough to destroy the Doctor once again.

Cybermen 
The Cybermen continued to attempt their takeover of Earth. Adric sacrificed his life to halt one of their many schemes for good.

The Master 
The Master would continue to plague the Doctor and the universe many times over this incarnation, though his demeanor and goals were less conquest-oriented and more destroy-the-Doctor-oriented.

Omega 
Omega attempted to break free of his black hole prison again, this time by bonding with the Doctor's physical form. As you may have guessed, it didn't work.

Silurians 
The Doctor ran into humanity's distant cousins several more times, often appearing with the Sea Devils, an aquatic offshoot.

Notable Traits 
Towards the end of 4's life, his mind kept dwelling on the idea of entropy, and lamented his long life, filled with meddling, and interfering, and dictating the course of history; it was a common theme in the last few stories, especially "Logopolis." And so, 5 was a younger man who would defer to the local authority as opposed to waltzing in and taking over the situation. He would help people, but he was less bossy about it. He was a more sensitive and empathic Doctor, and was the first one to begin to embrace pacifism. However, he would still use deadly force if he felt it was necessary. 

Catchphrases: 
"Brave heart, Tegan." 
"Sorry, must dash!"

Notable Character History 

The 5th Doctor's regeneration was not a smooth one. He suffered from bouts of amnesia and required a "zero room" (a room that was cut off from all outside influences of time and space) to recuperate. When they ended up converting the TARDIS's zero room into engine power to escape the Big Bang, they were forced to find an alternative: a place called Castrovalva. After the Doctor recovered fully, he exposed Castrovalva as a mental creation of the Master, and left him behind in his collapsing mental realm. He and his companions flew off into time and space, having many adventures fighting Cybermen, Silurians, Sea Devils, and more.

Adric sadly sacrificed his life to destroy the Cybermen's latest plan, and after another encounter with the Master (who was attempting to destroy the Doctor and fix his TARDIS) Tegan got left behind at Heathrow due to a misunderstanding (although she rejoined during Omega's scheme to return to this galaxy) and part ways with the TARDIS team again after the Dalek civil war incident.

Nyssa would also leave to help the inhabitants of Terminus fight a disease.
 
The Doctor ran into the Black Guardian again, and freed some of his minions from his control, meeting Turlough (who would leave after Peri joined), Kamelion (who died soon after), and Peri Brown, who stumbled into the whole affair when Kamelion impersonated her stepfather.

But while Tegan and Turlough acted as the TARDIS team, the Doctor did the most fangasmy thing yet. He teamed up with himself. Five times.

Or rather, the Fifth Doctor teamed up with three previous versions of himself and a wax figure of Tom Baker.

And they encountered Rassilon, the founder of Time Lord society, a now-dead messianic-ish figure who can turn evil men to living statues for all eternity. Awesome.
The Doctor and Peri would eventually make their way to Androzani Minor, where deadly cave fumes threatened to kill Peri. After getting her back to the TARDIS, the Doctor held his breath and ventured deep into the caves to retrieve the only cure: the milk of an indigenous bat. He returned with enough to cure them both, but ended up losing half of what he had. With no alternative that he could see, he gave the cure to Peri and began to die. After hallucinating the faces of his allies and enemies, the Doctor began to regenerate. 
And oh, boy howdy, did the spectrox toxaemia take its toll on his mind in his next regeneration....

Alternate Versions 
Well, there was the "Watcher."

Throughout the 4th Doctor's last story, he was assisted from afar by the silent, pale man dubbed "The Watcher." 
At the moment before his regeneration, the watcher joined with the Doctor to merge into the 5th Doctor. The idea was that the watcher was a quantum possibility between regenerations. 
Put simply, the 4 1/2th Doctor. 
Keep that in mind for later....

But now, we're about to enter a period of upheaval in the Doctor's history.
Upheaval and cancellation.