Lookups on Merriam-Webster.com started spiking on August 12, 2010.
When Elizabeth Gilbert, author of the best-selling memoir Eat, Pray, Love, appeared on "Good Morning America," host George Stephanopoulos called her "Julia Roberts' doppelganger."
As Stephanopoulos used it, doppelganger means "someone who looks like someone else," or simply someone's "double."
Since Julia Roberts plays a character based on Elizabeth Gilbert in the movie version of the book, it might be more accurate the other way around: Julia is Elizabeth's doppelganger. But since Julia Roberts is Julia Roberts, this made for a fancy compliment to Ms. Gilbert.
Doppelganger comes from a German word that translates as "double goer." It originally meant "a ghostly counterpart of a living person."