About 20 years ago as a budding video game critic, I made one of the biggest miscalculations possible in the field: I thought “Call of Duty” had no future.

I was in Los Angeles at the Electronic Entertainment Expo in 2003, and a uniformed Army soldier barked at me, “Hey, wanna play some ‘Call of Duty?’” He looked corny. The game itself looked like a copycat of the already-established Medal of Honor series, the first to evoke “Saving Private Ryan” in an action game.

I did not yet know that the creators of Medal of Honor jumped ship to publisher Activision to create “Call of Duty.” And I definitely did not yet know that the Call of Duty series would become one of the reasons video games have become the highest grossing entertainment business in the world.

“Call of Duty” released for PC platforms on Oct. 29, 2003, an ambitious video game made by a team of 27 people that aimed to mimic the feeling of boots-on-the-ground infantry action. Today, more than 3,000 people work on Call of Duty, a franchise with eye-popping earning power; last year’s “Modern Warfare II” pulled in more than $1 billion in revenue in 10 days. With more than 425 million copies sold in 20 years, Call of Duty is the fourth best-selling game franchise in history after Mario, Tetris and Pokémon. Since 2009, a Call of Duty game has been the best-selling game of almost every year.

Its latest game, “Call of Duty: Modern Warfare III,” releases in November, and will be the first title from publisher Activision Blizzard under its newest owners, Microsoft. The tech giant acquired the games publisher for $69 billion after more than a year of legal battles. In court filings, Sony PlayStation executives fought to keep the franchise available on their platform, citing its huge popularity with PlayStation players, and that the brand accounted for at least $1 billion in sales for Sony during 2021 (the exact figures are redacted).

Despite its lofty perch as one of the gaming industry’s golden geese, competition has driven the franchise to evolve its business model over the last two decades, said franchise general manager Johanna Faries, a former longtime marketing and business development executive for the NFL.

“There are so many different genres, so many different platform dynamics to consider,” Faries said in an interview with The Washington Post. “It’s all going to come down to amazing gameplay, that’s the core of the experience. But it also shapes how we think expansively about where we show up, and how do we partner with different verticals across different entertainment mediums so it’s really seeping into a bigger, broader conversation.”

Dissatisfied with publisher Electronic Arts, several “Medal of Honor” creatives in 2002 moved to Activision to form Infinity Ward, aiming to compete with a game concept they created. They succeeded: The Medal of Honor series is all but gone today, and Call of Duty became the premiere military shooter franchise. In a trilogy of games based on World War II conflicts, Infinity Ward crafted stories from different Allied Forces perspectives.

By the third game, early 20th century conflicts already felt like a tired genre. In 2007, Infinity Ward created “Call of Duty 4: Modern Warfare,” which not only became a smash hit success, it revolutionized how online multiplayer games are engineered, designed and monetized. Its influence remains inseparable from modern online games, from “Fortnite” to “Apex Legends,” the EA-published game by former Infinity Ward leaders who returned to the publisher.

“Modern Warfare” didn’t just become the template for online competition, it elevated the template. It moved faster like no other game on the PlayStation 3 or Xbox 360, it made finding other teammates easy, and it incentivized infinite replayability with the promise of new weapons and aesthetic bragging rights with online medals.

Gaming subcultures and businesses raced to keep up. “Modern Warfare” inspired a 14-year-old Atlanta boy named Keshav Bhat to start CharlieIntel.com, an online business covering Call of Duty news he created with a friend in June 2011 — an early example of a website and social media account dedicated to news around a single game franchise. Bhat said gaming news sites didn’t provide enough speedy coverage and he wanted to fill that need. In 2018, the site was acquired by Dexerto, a digital media company that covers gaming and esports. Now 27, Bhat is head of social media for Dexerto, and CharlieIntel on X (formerly Twitter) now boasts 3.6 million followers.

“Call of Duty’s legacy is bringing friends together to enjoy content online in a way that not many games were able to do,” Bhat said, adding that he started CharlieIntel to help centralize a once disparate online community. “I’ve met people in 2011 that I still talk to today thanks to Call of Duty.”

Call of Duty also became a rarity in the games industry: an annual release similar to sports games like the Madden or NBA 2K series. Bhat said that release schedule helped Call of Duty snowball to around 100 million players a month in recent years.

The series continued following the “Modern Warfare” template of selling new content like maps and modes in separate packages. It played with setting, using the Vietnam War and a fantasy sci-fi future as backdrops for narrative, and it kept selling.

In 2019, the series finally entered the smartphone space with “Call of Duty: Mobile,” an app downloaded 250 million times in its first year, according to Sensor Tower estimates. And in 2020, the series on PC and consoles introduced “Warzone,” which followed the free-to-play model pioneered by mobile games and popularized by “Fortnite.”

A-list celebrities like Kit Harington of “Game of Thrones” have starred in stories throughout the series. Today, “Warzone” is populated by players pretending to be Nicki Minaj, Snoop Dogg, 21 Savage and Bruce Willis. Celebrity tie-ins are part of the franchise’s attempt to broaden its appeal beyond its roots as a wartime simulator, particularly as ongoing real-life conflicts persist. (I couldn’t tell you how many girl friends of mine texted me asking me to teach them how to play a Call of Duty game so they could run around as Nicki Minaj.)

“[These options and features] only reinforce that this is entertainment, this is here to find and make friends after a hard day at work or school,” Faries said. “It’s really about joy and creativity at the end of the day.”