The Gatekeeper of the Nethersphere made a highly unexpected debut in "Deep Breath," but Doctor Who fans still don't know who she really is.

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Played by Michelle Gomez and slated to feature in the two-part season 8 finale, the Gatekeeper of the Nethersphere looks distinctly like Mary Poppins. Don't expect her to dole out spoonfuls of sugar, however. Gomez's character will have a little mischief up her sleeve, showrunner Steven Moffat recently teased.

"I've known Michelle for years, and I'm thrilled to welcome her to Doctor Who," Moffat said, according to Doctor Who TV. "She's everything we need - brilliant, Scottish, and a tiny bit satanic."

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Despite having a dash of the devil in her, it appears the Gatekeeper will partner with the Doctor (Peter Capaldi) during "Dark Water" and "Death In Heaven." As the cybermen seemingly try to convert the dead, the Gatekeeper was seen standing shoulder to shoulder with Twelve during filming.

Will Gomez's mysterious character be a villain or a hero? Tell us what you think in the poll below!

Find out more when Doctor Who airs Saturdays on the BBC and BBC America. Click the video below to see a preview for the series' next episode, "Into the Dalek."

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