Stella Schwartz, 16, hopped on the chess bandwagon earlier this year after hearing about the game from her older brother, Hugh, a high school senior in San Francisco. Alex Post, a freshman at the University of Colorado, started playing in February, after some chess-related videos appeared in his Tik Tok feed; then he got his whole fraternity playing.

Many other teenagers and young adults said that they too had recently developed a regular chess habit, although they could not recall how it started. But by all accounts from players, parents, teachers, website metrics the games popularity has exploded.

Sinceearly November, the number of daily activeusers to Chess.com, a website and app where visitors can get chess news, learn the game and play against one another and computer opponents, has jumped from 5.4 million to more than 11 million, rising sharply after the beginning of the year. (In December Chess.com also purchased the Play Magnus Group, a company started by chess world champion Magnus Carlsen that includes a mobile chess app.)

The biggest growth has come from players who are 13 to 17 years old 549,000 visited Chess.com in January and February, more than twice as many as in the two months prior, according to a company estimate of traffic. The second-fastest age group in the same period was 18- to 24-year-olds. Its everyone, every single day, Ms. Schwartz said. Ive seen people play at parties.

Casual observers, as well as newly avid chess players, may attribute the trend to pandemic lockdown and boredom, or perhaps to the popularity of the 2020 Netflix mini-series The Queens Gambit. But quietly a grandmaster plan was also unfolding, carefully crafted by Chess.com to broaden the appeal of the game and turn millennials and Gen Z into chess-playing pawns. Were they playing chess, or was chess playing them?

Everything was targeted right at high school, college and junior high, saidErik Allebest, chief executive officer of Chess.com.

The strategy was very much deliberate, he said: to erase the perception of chess as a grueling, geeky battle of wits and to package it instead on social media as less intimidating, fun, even funny. The matches offered on Chess.com also play to impatience. Timed games can be played at various lengths: 10 minutes, three minutes or, if that seems interminable, one minute. Still too long? Enjoy a 30-second match! Sometimes, Mr. Allebest said, its just about sport for sports sake, not about getting better.

Soon, before anyone quite knew what had happened, it was game over, and chess had won. It happened in a really short period of time, Mr. Allebest said of the games online growth, thanks to a handful of crazy seeds.

Happenstance the coronavirus, word of mouth, the handsomeness of Mr. Carlsen played a part. From February 2020 to February 2021, usage on Chess.com appsleaped from around1.5 million daily activeusers to around4.5 million.

Behind the scenes, Chess.com was working to change the games image and attract new players. This was good for business. Although the app allows users to play for free, its financial model relies on charging for tiers of service, from $6.99 to $16.99 per month for additional features like instructional videos and computer analysis of a players games and moves. The strategy, simply, was to rebrand chess as good old-fashioned fun.

When I was a kid, chess was for nerds, Mr. Allebest said. We started selling the enjoyment of chess and community more than just the top players and news of top players. In 2020, the site started hosting tournaments with online influencers who were not particularly adept at chess but had large followings among young people. These included xQc, a professional video-game player and streamer; Ludwig, an e-sports streamer; MoistCr1TiKal, another streamer and commentator; and Mr. Beast, a 24-year-old YouTube sensation with 147 million subscribers.

Chess.com hired college students to manage its social media presence. The students were encouraged to be irreverent and funny and to create memes, Mr. Allebest said. A recent blog post on the site was titled Why chess sucks and offered as the main reason, I always lose!

The sites Instagram account features short, offbeat videos, including the regular appearance of a bearded man in a puffy green pawn costume, who at one point trips over an electrical cord. Joker takes pawn.

Before long, an array of online chess personalities had emerged.

Levy Rozman, 27, is an international masterand a lively, charismatic commentator better known as GothamChess; Mr. Allebest described him as a chess prophet spokesperson for 14- to 25-year-olds. Grandmaster GMHikaru has 1.91 million YouTube followers. Alexandra Botez, 28, another chess celebrity on Twitch and YouTube, earned a particular claim to fame: Once, while streaming a match, she blundered into losing her queen and reacted with an endearing, bemused shock that made the gaffe seem cool. To accidentally lose your queen is now known as the Botez Gambit.

Mr. Post, the freshman at the University of Colorado, said he was drawn in by a bunch of clips TikTok videos by GothamChess at a moment when he was feeling kind of bored.

That was in early February; now, he plays every day, including sometimes in class. And he himself turned into a chess influencer. At a fraternity event, he said, he asked a frat brother, Yo, are you good at chess?

He said, Lets play, and then another dude said, Im decent, and it was like a domino effect, Mr. Post said.

Chess.com allows users to play against other people of their own skill level or against computer programs of various levels, including A.I. opponents that have names and personalities and can be outspoken.

Fabigi, described by Chess.com as a hardworking Italian American plumber, is an advanced beginner. Boshi, portrayed as a longhaired human with a reptile body, plays at the beginner level and is everyones favorite dinosaur sidekick, according to a Chess.com description.

But the mother of all Chess.com bots, introduced only for the month of January, was Mittens, an anime-esque tabby cat with big green eyes that look a little sad. Mittens was advertised by Chess.com as having a chess rating of 1 the worst. In reality, Mittens was a stone-cold killer with a sadistic streak.

Mittens was created with world-class skills and was unlikely to lose against the worlds top grandmasters. Mittens played slowly, appearing to give the opponent a chance while muttering odd and obnoxious taunts. (Meow, I am become Mittens, destroyer of kings.)

We made it strong enough to beat virtually every human player in the world, but not quickly, said Mike Klein, the chief chess officer of ChessKid.com, which is a part of the Chess.com company.

In January, 40 million games were played against Mittens, which Slate described in a headline at the time as the evil cat bot destroying players souls.

Mr. Klein has been traveling the country trying to convince schools to include chess in the curriculum. He argues that chess is good for the brain, but he concedes that the scientific studies he invokes, linking chess with better performance on standardized tests, are pretty old or dont have a good control group or are not a large enough sample size.

Whether chess offers anything more valuable than other online games do is unclear, said Dr. Michael Rich, an associate professor of pediatrics at Harvard Medical School and the founder of the Digital Wellness Lab, which studies the health aspects of technology use. It all depends, he said, on whether someone is playing with patience, and to learn, or just for quick digital thrills.

Some teachers complain that chess is more of a distraction than a learning tool. They play it constantly, schoolwide, and its gotten to the point where they arent turning anything in and are exclusively playing chess, an anonymous high school teacher said of students in a post on Reddit, where several threads have emerged on the subject. Mastery appeared to be an afterthought, the teacher wrote: The only thing is theyre all really, really bad at it? Theyre absolutely awful.

Ms. Schwartz, the high school sophomore in San Francisco, said that she generally avoided playing in class and that it did benefit her brain. Chess is a smart game, she said.

Her mother, Emily Stegner-Schwartz, agreed. Id rather she play chess than, whats that game, Jewel Crusher or Candy Land, she said, referring to the game Candy Crush. Online chess is to chess what pickleball is to tennis, she said.

Her son, Hugh, the high-school senior, couldnt recall what first got him playing on Chess.com earlier this year friends, maybe? I dont know, its weird, he said. Now he plays twice a day. And if there was a corporate strategy to capture him, did it really matter?

Everybody is manipulating people now on social media, he said. Chess is not the worst thing to be manipulated into.

Audio produced by Kate Winslett.

Read more:

The Stealth Campaign That's Getting Your Kids Hooked on Chess - The New York Times