World's most notorious nightclub bouncer had a very ironic role in John Wick 4

Keanu Reeves' legendary hitman ventures across the entire globe in John Wick 4, so I suppose it's only natural that he'd run into one of the most famous bouncers in the world while doing so.

Challenged with tracking down some of the underworld's most powerful players, Wick finds himself travelling from New York to Paris, Japan to Berlin in the latest instalment of the action franchise.

Meanwhile, in the real world, Sven Marquardt has been making a name for himself as the most iconic bouncer Berlin has ever seen.

The 61-year-old leads security at the entrance of Berghain; a techno club housed in a former East German power plant, and is notorious for turning away hopeful customers for the smallest discrepancy.

Long lines flow from the building and some attendees wait for hours, only to be turned away by the strict security at the door.

Marquardt's face tattoos and lip piercings make him instantly recognisable, so it didn't take long at all for fans to spot him when he made a surprise appearance on the big screen in John Wick 4.

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Berghain itself isn't explicitly mentioned in the film, but Wick finds himself at a club that looks to be very much inspired by the establishment when he stops in Berlin.

There, he finds his associate, Klaus, played by Marquardt.

While in real life the bouncer is all about crowd control, in the film he essentially does the opposite by helping Wick to locate the person he's instructed to assassinate, in turn sparking Wick's huge fight in the middle of the club.

Marquardt has only one line in the film, "I am Klaus," but that was all that was needed to delight fans.

"When Sven Marquardt said "I am klaus" in John Wick 4 I stood up and clapped," one fan wrote after watching the movie.

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Another tweeted: "Sven Marquardt made the Berlin scenes of John Wick 4 1000x more authentic."

Marquardt first began running security at Berghain when the club opened in 2004, and while customers are desperate to know the key to gaining entry, the bouncer has previously admitted that the choices are 'subjective'.

Speaking to GQ, he said: "Only a few of my guys are allowed to select guests at the door. They have to understand what Berghain is all about first, and I try to give them that foundation. Beyond that, there are no set rules.

"My people all have their own personalities, and you can see their sensibilities reflected in the crowd over the course of their shifts. You always want friction, though. That’s the theme in any good club: diversity, friction."

Marquardt's notoriety as a bouncer has helped him embark on a few other ventures over the years, including a stint as a clothing model for 44 Label Group and appearances as himself in various other movies and TV series.