Lewis Carroll's 1871 fable "Through the Looking Glass, and What Alice Found There" features a notable scene wherein the young titular protagonist runs across a pair of whimsically dunderheaded identical twins while lost in an alternate dimension. The characters are named Tweedledee and Tweedledum and are based on numerous 18th-century folk poems variously attributed to John Byron, John Pope, and Jonathan Swift. In an early epigram by Byron, the two characters agree to have a battle but are startled by a crow, and forget to fight each other. It wouldn't be until the publication of "Through the Looking Glass," and John Tenniel's illustrations therein, that Tweedledee and Tweedledum would be depicted as identical twins.
In Carroll's book, the twins reenact the Byron epigram and flee when a crow appears. Some might say that Tweedledee and Tweedledum represent easily distracted governments, or merely the capriciousness of children. Either way, Tweedledee and Tweedledum lodged themselves in the cultural consciousness and have been there ever since.
Tim Burton's blindingly successful 2010 adaptation of "Alice in Wonderland" wasn't so much a new telling of the story as a sequel. It featured a 19-year-old Alice (Mia Wasikowska) returning to Wonderland after a decade away, finding that the magical kingdom had succumbed to war and tyranny. Alice would have to take up a sword and fight the armies of the Red Queen (Helena Bonham Carter) to restore peace. She is also said to be destined to slay the Jabberwocky. Those days won't become frabjous on their own.
In Burton's "Alice," Tweedledee and Tweedledum were both played by actor Matt Lucas. Lucas' face could clearly be seen on screen, but the filmmakers used extensive motion-capture technology to turn them into bizarre, squat, egg-shaped beings. Matt Lucas also played Tweedledee and Tweedledum in James Bobin's 2016 sequel "Alice Through the Looking Glass."
Here's what he looks like outside the motion capture suit.