The BBC's Doctor Who is the longest running sci-fi series on television, after being on the air for more than 50 years. When it started out, it was shown in black-and-white and starred William Hartnell as the first Doctor, a grumpy old man from space who was quite brilliant and fought frightening alien creatures. Today, the series is going stronger than ever and stars Peter Capaldi as the Twelfth Doctor. But Capaldi's time is running out. After three great seasons, the last of which recently concluded, Capaldi has only one episode left before a new actor takes on the role.

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Soon, the Doctor will change, and so too will the series, when new showrunner Chris Chibnall takes the reins of the show. Doctor Who is known to be a series in constant flux, as much about endings and beginnings. But one thing that never changes in this series is who the Doctor is, down to his core: a hero. Some might even call him a superhero, a man with extraordinary abilities who does the impossible, time and time again. Today, CBR takes a look at 15 reasons the Doctor is the greatest superhero out there, whether they hail from Marvel, DC, Image or any other comic book.

15 HE GOES ANYWHERE IN SPACE AND TIME, SAVING PEOPLE

The Doctor wouldn't be complete without his big blue box, his ship that allows him to go anywhere in time and space. Time And Relative Dimension In Space -- or TARDIS -- is a spaceship that is also a time machine. He uses this great and powerful machine to travel anywhere he or the TARDIS likes -- it can have a mind of its own sometimes -- and one way or another, they always manage to find trouble.

But trouble only means that someone is in need of help, and that is all that the Doctor needs to know. No matter the threat -- whether it's natural like a black hole or a volcano, or physical like scary monsters or evil aliens hellbent on exterminating everyone -- the Doctor will not hesitate to put himself in harm's way if it means saving anyone he can.

14 HE IS IMMORTAL (SORT OF)

The Doctor is a Time Lord, a race of beings that have the power to regenerate their bodies, something that grants them an incredibly long lifespan that goes well into the thousands of years. When it comes to life, the Doctor is more than a few thousand years old, and that is without mentioning the billions of years he spent trapped inside his own Time Lord confession dial, as seen in the season nine episode Heaven Sent.

When it comes to death, the Time Lords regenerate, their bodies healing themselves and taking on a new face to go along with it. While a regular Time Lord usually has 12 cycles of life, or 12 regenerations, the Doctor was given a new cycle of regeneration energy, one that could potentially give him even more than 12 new regenerations. This Doctor will go on to live for thousands of years more, and he will always have the wisdom that comes along with it.

13 HE HAS SAVED COUNTLESS WORLDS AND MILLIONS OF PEOPLE

Doctor Who has been on television for 53 years and 839 episodes so far, which means that the Doctor has saved the day at least 839 times. From all corners of the universe, whether it's in the past, the present, the future, in alternate timelines and parallel or pocket universes, the Doctor has faced overwhelming odds and in doing so saved countless worlds -- entire planets filled with life.

The Doctor has never stopped to count how many he has saved, but over his many lives, it's safe to say that that number is well into the millions, if not billions. But numbers were never important, because to him, the one is just as important as the thousand. He can sacrifice it all, put it all on the line, just to save one life. Or one planet. It makes no difference to him, simply because he is a good man.

12 HE HAS A WICKED COSTUME

While The Doctor may not have a traditional superhero costume filled with vibrant colors and spandex, he still has his very own outfit that makes him instantly recognizable. What could appear to be plain clothes, mixed together with a unique touch or twist form a look for The Doctor that is as much a part of him as his TARDIS.

All 12 incarnations of the Doctor have had a particular look that has set one apart from his other selves. The first Doctor? Hat and white scarf. The fourth Doctor? The multi-colored scarf. Tenth? Striped suit, tie and long coat. Eleventh? Bow tie, of course. And finally, the current incarnation of the Doctor, the twelfth, the magician's coat and sunglasses. With each incarnation, the iconic outfits are a reflection of their very own personalities.

11 HE HAS AN EXTENSIVE ROGUES GALLERY

Just like any long-running superhero, The Doctor has a long list of enemies to his name, a list that only grows longer with each new season of the show. These villains range from the recurring and instantly recognizable -- like the Daleks, the Cybermen and the Weeping Angels -- to the more rarely used, yet equally frightening -- like the Ice Warriors, the Silurians and the Zygons.

Each of these enemies have been a part of the show for a very long time and The Doctor, just like Superman or Batman and their respective foes, have faced and defeated them countless times before. The number and originality of these villains only grow bigger, as each new season brings with it completely new and original threats and monsters like the Silence, the Whisper Men and the Monks for The Doctor to face and defeat.

10 HIS HUMAN COMPANIONS GROUND HIM (LIKE SIDEKICKS)

Like so many great heroes, heroes who face insurmountable odds and ultimately win out the day, heroes who pass judgments of life and death and who have the power to bring about great change, The Doctor can sometimes forget his own place or succumb to his own emotions of anger and loneliness. Traveling the spaceways alone for hundreds of years can do that to a person.

That is why The Doctor is always surrounded by a companion. In some cases, companions. All of them are human, so that they can be there for him or be there to stop him if he's ever going too far, so that they can keep his feet on the ground and remind him what he's fighting for. With them by his side, there's nothing The Doctor won't do, moving Heaven and Earth included, to be the hero they expect him to be.

9 HE HAS THE COOLEST SUPERHERO GADGET EVER

If a superhero doesn't have superpowers, then there's a safe bet that he has a few weapons in his arsenal to help him fight the bad guys and save those in danger. But The Doctor is different from the rest, because he hates weapons; guns especially. The only thing he carries around with him is the Time Lord scientific instrument known as a Sonic Screwdriver.

While not an offensive weapon, the Sonic Screwdriver can be used for many applications like scanning and analyzing, hacking and reprogramming computers, unlocking doors and activating/deactivating anything that has circuitry inside it. Like the original Green lantern's ring, it doesn't work on wood (every weapon has its weakness), but when used correctly, the Sonic Screwdriver can be the most useful gadget to have around. With it, The Doctor has managed to save the day countless times over.

8 HE IS FEARED THE UNIVERSE OVER

Over all of his many adventures, all of the people, races and planets he has saved, all of the villains he has defeated, The Doctor has formed a reputation across the galaxies, a reputation that many alien creatures and races who would do others harm have come to fear. It has even come to a point that the simple name of "The Doctor" can stop an army in its tracks and send a full fleet flying back.

But while his name might strike fear into would-be conquerors, it also brings something much different to those who are oppressed, those who are at the mercy of evil and those who are helpless. The Doctor, with his blue box, has also become a source of hope across the stars. A savior for all. And if they do not know him before, they will tell his stories when he has gone, spreading his legend.

7 HE WAS THE LONE SURVIVOR OF HIS RACE (BUT SAVED THEM ALL)

Doctor Who saw a whole new wrinkle added to its primary hero when he resurfaced under new leadership, and in his ninth incarnation in the first season of its modern revival. He was now the lone survivor of his race, the Time Lords, who had been wiped out in a great war. For a very long time -- and three incarnations -- The Doctor carried the weight of the loss of his race everywhere he went, a darkness that was now a part of him.

But when fate presented him with an opportunity, he made it possible, thanks to his other selves, to combine all of his previous incarnations and save the entirety of his race, and his home planet. Doing so broke all the rules space and time imaginable, but it was a testament to how truly good a man he was, how heroic he was and how, against all odds, he found a way, once again, to save everyone.

6 HE IS THE PRESIDENT OF THE WORLD

When a terrible crisis befalls planet Earth, when an attack on the level of alien invasions occur, the Unified Intelligent Taskforce (or UNIT for short) has the worldwide authority to name a President of Earth to represent all governments and nations and command every possible army in the world should the need arise. And UNIT has only one candidate for the position: the Doctor.

Thanks to his past dealings with the agency and the fact that he has saved the planet itself -- as well as the human race -- hundreds of times, the Doctor has been named President of Earth during full-scale attacks and incursions that threatened the human race itself. While it's not a position he likes or takes lightly, he does understand the need for it and is willing to do whatever is necessary to save the humans.

5 HE IS CUNNINGLY BRILLIANT

The Doctor is at his core an adventurer, a good man who wants to see the universe, old and new, far and wide, from top to bottom. Through his long life and many adventures, there is one thing that has gotten him out of the grasp of the most dastardly of villains and the most terrible traps of death. And it wasn't his Sonic Screwdriver or his TARDIS. It was his brilliance.

Long has he stated that there is one thing one must never put in a trap, and that is his own self. Because no matter the circumstances, no matter the odds, the Doctor finds a way. It's what he does. He knows everything there is to know about alien science and technologies, any culture and belief possible in the universe and almost everything about life and death, and he puts it all to good use.

4 HE HAS A NEMESIS

Like Batman and the Joker or Superman and Lex Luthor, the Doctor has an equal, an opposite, a nemesis; an enemy who is just like him, yet so very different. He is the other side of the Time Lord coin. In the Doctor's case, this person is known as the Master. A person who was his friend a long time ago, The Master is just as brilliant as he is, but infinitely more devious.

While the Doctor is on the side of good and life, the Master is all about evil machinations and death. The two share a long storied past, with many confrontations that saw the Doctor fall on the losing side, only for him to return stronger and defeat his nemesis. But like all good heroes, the Doctor cannot bring himself to kill his enemy, because he also values life... especially that of a friend.

3 HE HAS SUFFERED MANY GREAT LOSSES, BUT KEEPS FIGHTING

One of the downsides of being a nearly immortal Time Lord is that while the Doctor has many human friends and companions, he also comes to lose them. Some he has to leave behind, others choose to put an end to their travels with him, while others have paid the ultimate price while they were under his care. His is a story filled with endings. And he doesn't like endings.

His losses, be they of his friends, his family, his race or his wife River Song, end up leaving him alone, where he lives for long periods of time in self-imposed exiled. But something, or someone -- like current companion Bill Potts -- always comes along to remind him of who he is and what he does, and how joyous exploring the universe can be. These losses all weigh heavily on him, but he finds the will to keep going. He moves on.

2 HE REBOOTED THE ENTIRE UNIVERSE WHEN IT WAS DESTROYED

In the fifth season of Doctor Who, the TARDIS had locked itself in a time loop as it was destroyed; the explosion caused every star in the universe, past and present, to go out. The only way to save the universe was for the Doctor to use the Pandorica, the perfect prison that had been built to contain him, to restore and extrapolate the atoms it contained.

However, to re-spark the universe, in order to have it be reborn with a second Big Bang, the Doctor had to sacrifice his own existence. Being sealed out of this new universe, the Doctor didn't die, he simply had never existed. It was only thanks to his trusted companion Amy Pond that he was able to come back to reality, as the man who was ready to give everything up, even his own existence, to save the entire universe.

1 HE HAS DIED AND SACRIFICED HIMSELF MANY TIMES OVER

One thing that is important to know about the Doctor's regeneration ability is that while it prolongs his life, it also allows him to experiences birth, life and death. When he changes bodies, his personality also changes. He becomes a new person, and it's a process that he has come to hate, because he gets used to the person he is, and sometimes he isn't ready to let go and become someone else.

But while the process of being reborn and facing death is alarming, even to the Doctor, it's something he is willing to face in order to save someone. Many times his regenerations have come as a price to pay after he had sacrificed himself to protect others, to save his friends and his companions, knowing full well what it would mean for him. And that, above all else, is what makes him the greatest hero of all time. And space.

Who is your favorite Doctor, and do you think he is the best superhero ever? Be sure to let us know in the comments!