Doctor Who's Steven Moffat will not take the search for a new companion lightly.

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The iconic BBC series may be named for it's Time Lord lead, but the Doctor's co-pilot and stalwart partner is as integral to the show as the TARDIS itself. Now that Clara (Jenna Louise Coleman) is out of the picture, Moffat is tasked with finding the perfect actor/actress to keep Peter Capaldi's Twelve on his toes.

Once this new companion is cast, viewers can expect Doctor Who to get a tonal shakeup.

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"I'm still [in] the quite early stages [of casting]-but very clear on the change we're going to make to the tone of the show," the showrunner told Digital Spy. "Because the tone of the show is so driven by what we call the companion, it's so driven by that. It's not just casting a supporting character. It's not. It's the lead or the co-lead, and it will become their story. So, it's a huge, massive thing."

Who do you think will make for a good companion as Doctor Who launches into its next chapter? Tell us in the comments below!

Doctor Who will return to the BBC and BBC America later this year. Click the video below to see a preview for the series' latest episode, "The Husbands of River Song."

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