The YouTube personality with the most subscribers isn’t Justin Bieber (8 million) or Rihanna (12.5 million). That honor goes to a 24-year-old Swede named Felix Kjellberg, better known by his YouTube handle, PewDiePie.

PewDiePie doesn’t sing or dance, no. PewDiePie has made his name—and a fortune—posting videos of himself playing video games. In one November video, for instance, he plays the Xbox Indie game “Techno Kitten Adventure,” helping a feline avatar navigate dangerous terrain filled with unicorns and narwhals, and shrieking in frustration each time his cat crashes into an obstacle.

“What am I supposed to do?” he wails shortly before his grey kitten with a jetpack dies. “It doesn’t get more hardcore than this.”

In another, featuring the game “Trouble in Terrorist Town,” PewDiePie controls a military gunman who gleefully mows down other soldiers. Together, these two clips have attracted nearly 7 million views.

In his videos, PewDiePie laughs, swears, and goofs around as if he were hanging out with his best friend. But 23 million people subscribe to his YouTube channel.

PewDiePie is a Let’s Player, one of hundreds of gamers who post “Let’s Plays” online (as in “Let’s Play Super Mario Bros.” or “Let’s Play Grand Theft Auto”), videos that are part “Mystery Science Theater,” part Siskel and Ebert reviews. As a Let’s Player navigates a game, he (or more rarely, she) provides running commentary, usually funny and profane.

Difficult as it may be to believe that online audiences throng to watch strangers play video games, Let’s Plays have surged in popularity. The top five Let’s Players collectively have more YouTube subscribers than Peru has people. A user-generated Wikia page tracking current Let’s Players, their subscriber totals, and their videographies lists about 950 players with active YouTube channels, collectively followed by more than 60 million subscribers. And the Wikia page acknowledges that this isn’t a comprehensive list.

Let’s Players aren’t driven only by love of gaming. Many hope to one day make a living playing games on YouTube; a few already do. PewDiePie’s estimated monthly revenue from YouTube ads fluctuates between $140,000 and $1.4 million depending on viewership, according to Social Blade, a company that monitors YouTube channels.

Other players bank much smaller paychecks. Matthew Varrone, 20, makes between $600 and $1,000 a month in ad revenue from his videos—not enough to rent an apartment, so he still lives with his parents in Milford, Connecticut—but still impressive considering he earns it doing something millions of people do every day for fun, for free. His YouTube channel, “Awesomefaceprod,” has drawn 20,000 subscribers since he started Let’s Playing in 2011. He’s otherwise unemployed, and hopes eventually to support himself by playing video games.

Because YouTube’s advent eight years ago made it possible, albeit unlikely, for young gamers to become millionaires, online talent agencies, dubbed “networks,” have sprouted around the Let’s Play phenomenon. PewDiePie’s network, Maker Studios, a Hollywood media company, provides marketing and publicity exclusively for “YouTube artists,” taking a cut of the proceeds. Maker Studios, like the company that represents Varonne, Fullscreen, Inc., represents various kinds of YouTube content creators, such as gamers and musicians.*

Although players realize that their chances of making millions are slim, many plan to parlay the skills they’ve acquired on YouTube into careers in video editing, game testing, or software design.

Typical of Let’s Players, Varrone’s interactions with viewers, other players, and Fullscreen take place entirely online. He has never visited the Fullscreen office in Los Angeles, met an employee in person, or even talked to one by phone.

“A lot of my life now exists online,” Varrone told me. “It’s pretty weird. I don’t know if that’s a good thing or not.”

He does hang out with other Let’s Players at gaming conventions—such as the upcoming Penny Arcade Expo East (PAX) in April in Boston, which drew 80,000 visitors last year—and considers some his closest friends despite almost never encountering them in real life.

Also typical of most Let’s Players, Varrone was on the receiving end of a copyright claim. Over three years, Nintendo filed Content ID claims against 15 of his videos, and those videos’ ad revenues now go to the company instead of him.

Publishers use YouTube’s Content ID system to identify use of their intellectual property. If a video contains content that matches a publisher’s ID, owners reserve the right to monetize, block or track the user-generated video. In more extreme cases, YouTube will remove a video, or an entire channel, if a publisher files a Digital Media Copyright Act (DMCA) complaint.

Players often face such threats of legal action. Although their videos help promote companies like Nintendo, and Let’s Players argue that they’re protected by fair use, the gaming industry isn’t thrilled about Let’s Players siphoning ad dollars from its intellectual property.

But murky legal issues haven’t prevented gaming videos from drawing a huge chunk of YouTube’s audience. Four of the top 10 YouTube channels ranked by Social Blade are gaming channels run by Let’s Players. Players started uploading gaming videos to YouTube almost as soon as the site launched in February 2005. As its popularity swelled, so did Let’s Plays; today 95 percent of all gamers flock to YouTube for information and entertainment, according to a Google report last year.