This Saturday, the Doctor is in. What doctor? Doctor Who.

For those who don’t know Doctor Who, it’s the longest-running science-fiction show in the world.

It follows the adventures of the Doctor, an alien blessed with multiple regenerations (which allows for different actors to play the role), as he travels through time and space in his time machine, the TARDIS.

Along the way, he fights, meets historical figures and often ends up enthusiastically talking about life and existence.

Since its return in 2005, (it first premiered in 1963 and ended in 1989)the show’s fandom has spread from a niche group to audiences worldwide. People are watching the show, and the show is helping to open viewers’ minds to unconventional and nerdy stories.

Saturday’s premiere, which marks the beginning of the show’s sixth season since its return, will probably be a hit. Matt Smith, the 11th actor to play the Doctor, will return, and current show runner Steven Moffat, a man as gifted at scaring audiences as he is at writing witty dialogue, is writing the episode.

Add in the 1960s setting, on-location filming in the United States (the first time principal photography has shot here), Richard Milhouse Nixon and a scary spacesuit-wearing monster, and you have what should be an entertaining show.

It’s the age of the geek, and Doctor Who’s one of the major players in spreading geek culture.

But what’s strange about Doctor Who is that for a long time it was aimed more at kids than a wider audience.

The show was originally designed to teach kids about history and science, and it was never a headliner or primetime darling. But recently it has spread to the United States, quickly accumulating a strong following that’s growing with each new season.

So how did this show go mainstream so suddenly?

The Doctor is a science hero, not an action hero. There are big explosions, monsters and plenty of chase scenes — Steven Moffat is the king of terrifying adventure stories — but unlike previous mainstream heroes like Rambo or any Schwarzenegger role, the Doctor triumphs through his intellect and a definitely geeky, hyper- enthusiastic love of exploring the universe.

But part of what makes the show so successful — and why it has been able to reach an audience beyond fans of science fiction — is that it’s fun.

No matter how dark the series gets, or how scary the monsters can be, there’s an air of adventure and optimism in every episode.

So many shows today, like Fox’s upcoming Terra Nova, are self-conscious about their geeky elements, like time travel and monsters, and always try to justify those elements, saying the show is more about the story or that those elements don’t matter compared to the political overtones and sexual nature of the content. Maybe they should take a cue from Doctor Who and just embrace their geekiness.

When Russell T. Davies brought Doctor Who back, the show was an oddity. Serious shows like Lost and 24 dominated the airwaves, all trying either to be topical or to reflect the tenseness of contemporary times.

There are no dramatic ethical questions or allusions to terrorism or the like. At a time when mainstream television, however engrossing, was at its most depressing, Doctor Who offered a cathartic adventure each week.

What separates Doctor Who from other shows is it embraces its sci-fi setting and features less melodrama and formulated storyline. By all accounts, the mainstream should have ignored it.

But it didn’t. The Doctor himself has become a geek icon, and now a mainstream icon as well.

Not bad for something that started as an educational show for children.

Nicholas Slayton is a sophomore majoring print and digital journalism. His column, “Age of the Geek,” ran Fridays.