If you're new to Doctor Who, one thing that might confuse you is that the Doctor is played by different actors. In fact, a total of 13 actors have taken on the role through the show's 50-year history, with five of those stints happening during the new version of the series that started airing in 2005.
But why does the Doctor often have a new face? How does the series explain this confusing process — and how does it impact the show?
What is regeneration?
This process, called regeneration, is an important part of the series' history, as well as its ongoing 50-plus-year plotline. Regeneration happens when the Doctor dies — actually, he doesn't die, he just "regenerates" into a different person.
Confused yet? Because the new person the Doctor regenerates into is still the Doctor, with all his thoughts and memories. However, this new person has a completely different face and body, along with a new personality. So while one Doctor is happy-go-lucky, the next might turn out grumpy and irritable.
Regeneration isn't unique to the Doctor: it's something that any Time Lord or Time Lady can do. It isn't limited by gender, either, as Time Lords and Ladies can regenerate as male or female (which explains how the Master became Missy last season).
The history of regeneration
In the 1960s, the first Doctor, actor William Hartnell, suffered from a deteriorating health condition associated with his age. This made it difficult for him to work, resulting in the BBC having to replace him. Rather than pull a "Bewitched," though, and simply bring in a new actor without explanation, Doctor Who writers came up with a better idea: regeneration. So when the first Doctor "died" from exhaustion, he became the second Doctor, portrayed by actor Patrick Troughton.
Eventually, Troughton left the series, so yet another Doctor took his place — the third Doctor, Jon Pertwee. And so on and so on. In time, the series started adding more detail to the regeneration process, and it has now become a part of the show's off- and onscreen history.
So what started out as a practical problem actually led to an important part of the Doctor's story, as well as giving the series a way to constantly keep itself fresh and new. Without regeneration, it's likely that we wouldn't have Doctor Who today.
Regeneration is important to the series' dramatic elements
Another effect of regeneration is that it adds additional dramatic tension to the series. Imagine the horror of having to say goodbye to all your loved ones only to become someone else. Imagine the strange feeling of having a new body that you have to get used to all over again. Imagine trying to explain how you're still the same person, but not, to the people who matter to you.
And regeneration doesn't always go smoothly. Sometimes, there's a transition period in which the body attempts to recover from what is a very complicated physical process.
Meanwhile, the Doctor's companions have to understand that the person they've grown to care for (and often love) is not the same person anymore. Imagine being in love with a young carefree Doctor, only to discover that he's now an older grumpier version of himself who can often be cruel. Imagine having to say goodbye to the Doctor over and over, because each one is his own persona.
Regeneration doesn't just offer the series a way to occasionally change things up — it also allows the series to explore the dramatic impact of what happens when the Doctor goes through this physical and mental change.
Regeneration can also impact the viewer, often leaving Doctor Who audiences in emotional turmoil — until they find they like the next Doctor. A good example of this is when the 10th Doctor, portrayed by David Tennant, told the audience that he didn't want to go — a scene that was as emotional for fans of the series as it was for the Doctor himself.
Doctor Who returns to BBC and BBC America for Season 9 on September 19.
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