The undercut is a hairstyle that was fashionable during the Edwardian era, 1920s, 1930s, 1940s, and 2010s predominantly among men. Typically, the hair on the top of the head is long and parted on either the side or center, while the back and sides are buzzed very short. It is closely related to the curtained hair of the mid and late 1990s, although wearers of undercuts during the 2010s tend to slick back the bangs away from the face.
Historically, the undercut has been associated with poverty and inability to afford a barber competent enough to blend in the sides, as on a regular haircut. From the turn of the 20th century until the 1920s, the undercut was popular among young working class men, especially members of street gangs. In interwar Glasgow, Neds, the precursors to the Teddy Boys, favoured a haircut that was long on top and cropped at the back and sides. Despite the fire risk, lots of paraffin wax was used to keep the hair in place. Other gangs who favored this haircut were the Scuttlers of Manchester, and the Peaky Blinders of Birmingham, because longer hair put the wearer at a disadvantage in a street fight. 
During the jazz age of the 1920s and 1930s, hairstyles of this type were considered mainstream fashion. In Nazi Germany, a version of this haircut which was long on top but shaved at the back and sides was popular among Wehrmacht officers.
Beginning in the late 1980s, centrally parted undercuts, derived from the bowl cut, made a comeback among fans of new wave, synthpop, and electronic music as an alternative to the mullets and backcombed hair worn by glam metal bands. A collar-length version of the haircut, known as curtained hair, went mainstream in the early 1990s and was worn by many celebrities, most notably Tom Cruise.
Curtained hair and undercuts went out of style in the early 2000s, but underwent a revival in the early 2010s among indie kids and the skater subculture who imitated the 1930s and 1940s version: longer and pomaded or swept to one side on top and shaved or clipped at the sides. At the time, although the style had many different names, one of the most controversial was the "Hitler Youth," "Jugend," or "fasci." Some of the most high-profile early adopters of this haircut included rapper Macklemore, North Korean dictator Kim Jong Un, soccer star David Beckham, and Win Butler, a singer with Arcade Fire.
By 2014, the haircut had become relatively mainstream in the UK and was worn by people not normally associated with the indie scene, such as reality television celebrities from shows like The Only Way Is Essex. A longer version of the haircut with long bangs, inspired by dubstep disc jockey Skrillex, pop star Miley Cyrus, Kelly Clarkson, and Rihanna, became popular at the same time among American ravers, hipster or scene girls, and female British chavs.
During the mid 2010s, some British schools have banned the so-called Hitler Youth cut as an extreme hairstyle. In America, the undercut is commonly associated with Alt-right activists like Richard B. Spencer, and with neofascist supporters seeking a less intimidating alternative to the buzzcut. TV host Samantha Bee was recently forced to apologise after calling the haircut of a recovering cancer patient "Nazi hair."
In popular culture
During the late 2000s and early 2010s, undercuts were often associated with villainous movie characters such as Hannibal Lecter in Hannibal Rising, with Johnny Depp's portrayal of gangster John Dillinger, Jared Leto as The Joker in Suicide Squad, Guy Pearce as the corrupt prohibition agent in Lawless, and with various German officers in war films.
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