Sole Surviving Scientist

It's After the End, humanity is on the brink of extinction. In a remote outpost somewhere, one man is still looking to reverse this situation. He toils away in a laboratory trying to cure the disease, fix the Earth's Magnetic field, change the weather, or even build a time machine to go back and prevent the apocalypse.

The Sole Surviving Scientist needn't be completely alone, he might have some soldiers guarding him, a few survivors he's generously allowed into his stronghold, even an assistant. Regardless of his company he's the only real scientist left (that we know of).

Often the scientist's efforts are fruitless and he descends into depression, madness or a macabre obsession with studying mankind's downfall.

This trope is especially common in zombie fiction.

Examples of Sole Surviving Scientist include:

Anime and Manga

Bulma in Dragonball Z, who invented a time machine to send Trunks to the past and find a way to kill the androids.

Comic Books

There was a 28 Days Later spin-off comic with a scientist who played a role in the creation of the Rage Virus. He admits this to a girl that he had escaped a holding facility with, and plans to atone by becoming one of these, being that he's one of the few people alive (maybe the only one) who knows anything about the virus and has the best chance of curing it. Unfortunately, she had lost her parent earlier during the initial outbreak, and lost her brother during the escape. Apparently learning that the guy she'd been helping was the root cause of those things is too much for her, so first she kisses him, then grabs his gun and shoots hims. Then lets herself be killed by the soldiers pursuing them. So much for that.
BPRD: When the Bureau gets its new headquarters, a disaffected nuclear-proof bunker in the mountains, they find an old scientist whose been living there since its was shut down, writing down notes on a typewriter for so long the keys wore out and it punched holes in the paper, he was so far gone he didn't notice. He later releases an Eldritch Abomination into the base thinking it some kind of angelic creature.

Film

Dr. Logan from Day of the Dead is a prime example. His obsessive pursuit of understanding the undead was a harsh critique on the pursuit of scientific knowledge without practical application.
Dr. Robert Nevil from the film version of I Am Legend is about as alone as you can get.
The future in-a-bubble scenes from The Fountain appear to be this trope, although the oncologist is more concerned with staying alive until he reaches a far-off star than with restoring the Earth.
Zac Hobson in The Quiet Earth, a scientist who was working on Project Flashlight. A malfunction caused almost everyone on Earth to simply disappear. He goes a little crazy in the first part of the movie, but after meeting two other survivors he tries to destroy the laboratory where the experiment took place so it can't happen again.
Abby in Grindhouse: Planet Terror Or he would have been if he hadn't gotten killed. This is lampshaded in the movie.

Cherry Darling: I don't suppose anyone else here is a bio-chemical engineer?

Literature

Edmond Haminton has a story where all the humanity has died except for a single immortal scientist. See Came Back Wrong for a description of his efforts.
In the Doctor Who spin-off novel The Eyeless, the Doctor visits a planet where most of the population was wiped out in an incomprehensible catastrophe. Professor Jeffip does his best to fill the Sole Surviving Scientist role.

Live-Action TV

Dr. Edwin Jenner from The Walking Dead is a depressed and ultimately suicidal scientist found alone in his compound by the other survivors.
Doctor Who: Professor Yana in "Utopia," until the Doctor shows up. The sole scientist at the end of the universe trying to get a rocket ship to work, so he can send everyone to Utopia.
Battlestar Galactica: The Final Five were Earth-1's sole surviving scientists after a nuclear holocaust, who attempted to Fling a Light Into the Future, only to succumb to the next iteration of the cycle of violence at the hands of their progeny.

Tabletop RPG

Maid RPG. In the replay "Maids at the End of the World", there was a worldwide nuclear war that wiped out civilization. The Master is Masami Onji, an Omnidisciplinary Scientist dedicated to finding a way to restore the Earth.

Theatre

In the play R.U.R. (a.k.a. Rossum's Universal Robots), after the robots kill off humanity, the sole survivor is Alquist. It is a significant plot point that Alquist is actually not a scientist at all; the robots want him to figure out how to allow them to reproduce, and he doesn't have the knowledge or skill to do so.

Video Games

In Metroid Prime 3, on the planet of Bryyo, you can read the journal entries of the last surviving scientist, as he tries to keep the world from suffering an environmental collapse. He fails.
A clear example is Belthasar from Chrono Trigger, how built the Epoch which would allow anyone to travel back in time and avoid the Earth's destruction by Lavos.
The Adobe Flash game One Chance is all about this - you play a scientist trying to fix an accidentally lethal cure for cancer as it slowly infects everyone in the lab.
In another Flash game, Lab of the Dead, the main character is a sole surviving researcher following in the footsteps of the original dead scientists.
Adam Fenix is Sera's Sole Surviving Scientist in the Gears of War series.

Web Comics

Othar in Girl Genius has been that but managed to go back in time (according to his Twitter, anyway).
- Tarvek in the same Twitter may have been a better example, since he sent Othar back and was much closer to the problem (while Othar metaphorically "slept through it").

Western Animation

Vandal Savage ends up a sole surviving scientist in the episode "Hereafter" from Justice League.