Editor's Note: Inc.'s 12th annual 30 Under 30 list features the young founders taking on some of the world's biggest challenges. Here, meet Karen X.

Web video is the medium of the moment. And Karen X. Cheng is the kind of talent who seems made for it. She's a one-woman creative agency, known as Karen X, who writes and directs viral videos for brands as varied as Brawny and 24 Hour Fitness. Her videos have attracted millions of hits.

Did she ever expect to get into this line of work? "No, absolutely freaking not!" Cheng says. In 2012, the 29-year-old entrepreneur announced her resignation from Microsoft by writing lyrics about her team, performed as a parody of "American Pie." Cheng posted the video on YouTube so that she could email the link to her colleagues. It wasn't long before TechCrunch found the video, which has now gathered more than 400,000 views.

Cheng later went on to launch a motivational app called Giveit100. Users would film themselves working every day on a new skill, like lifting weights or playing the flute. Then, after 100 days, the clips would be stitched together into an inspiring compilation. Unfortunately, it lacked a proper business model. "That was the first time that I failed in a major way," Cheng says.

All the while, Cheng had been shooting and promoting viral videos, in an effort to draw attention to Giveit100. One of them was "Girl Learns to Dance in a Year," which went absolutely viral, thanks to strategic promotion. The video hit 8.1 million views. Even after Giveit100 tanked, Cheng's interest in making videos remained.

In 2014, during a period of "funemployment," as she puts it, Cheng invented the "Donut Selfie," a sort of dance that involves filming yourself using a camera that swings around your head. That video also attracted attention (it currently has more than a million views), including from the marketing team at Beats by Dre. The company reached out to Cheng and offered to send her some free headphones. Her reaction? "Sure, why not," she recalls. Beats' VP of marketing flew out to meet her for drinks at a bar in San Francisco. Beats was interested in using her "Donut Selfie" concept as the basis for one of its global advertising campaigns. Cheng ended up signing an NDA.

The campaign moved fast. Within a month, Cheng starred in a commercial alongside Kylie Jenner, Nicki Minaj, and a host of other celebrities. Cheng soon realized that her knack for coming up with ideas that could go internet-viral was a viable business. Not only was she good at sparking the initial concept; she had also developed a system for getting the content to spread once it was published.

In January 2017, Credit Karma's Facebook page posted a video that Cheng created for it. Despite the dry subject -- tax preparation -- it racked up 7.9 million views and was mentioned in Advertising Age.

These days, Karen X is a boutique marketing firm that offers both consulting and video-creation services to select clients. So far this year, Cheng has run official campaigns for roughly six clients, but maintains a stable of about 20 in total. "I think in Silicon Valley, it's really easy to fall into this trap of grow, grow, grow," Cheng said, but she keeps the organization lean on purpose.

The stress of running a VC-backed startup -- especially one that failed -- taught Cheng that she wanted a different kind of business. "I'm able to access a level of talent that I couldn't if I were hiring full time," Cheng says. She marshals a slew of creative contractors, including video editors, lighting directors, storyboard artists, composers, and PR researchers.

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