When it was released in 1996, Pokémon made zealots of children. Desperate to catch ’em all (as the slogan goes), they would queue for hours, play truant from school (‘Pokéflu’ apparently), fight, steal and bankrupt their parents. Exasperated schools banned the trading cards; jittery parents fanned the flames of moral panic.

In November 1999, as the phenomenon reached its climax, Pokémon graced the cover of Time magazine; the accompanying feature described Pokémania, the fanaticism the game franchise inspired, as “a multimedia and interactive barrage like no other before it” and, less flatteringly, “a pestilential Ponzi scheme”. Eventually – outside Asia at least – Pokémon, like most children’s fads, faded from the mainstream.

“When I started my website back in 2003, Pokémon was dead,” says 30-year-old Jon Sahagian, editor-in-chief of the fansite pokebeach.com. “People in schools didn’t talk about it and scoffed at me and the few other fans who ever expressed any kind of interest in it.”

Yet Pokémon somehow continued to maintain a dedicated fandom; enough to see it estimated to be the highest grossing media franchise of all time. Now, with the release of Detective Pikachu, starring Ryan Reynolds, this month, the franchise gets its first ever live-action film. Not only is it expected to be a box office hit (and potentially the most successful film based on a video game ever), early reactions indicate it is cleverly positioned to appeal to both die-hard fans and those who don’t know their Squirtles from their Sobbles. The stage is set for Pokémania to return.

Unsurprisingly, Pokémon passed Bill Nighy by in the 1990s. The 69-year-old actor was, by his own admission, “generationally disqualified” from Pokémon. In fact, when he took on the role of anthropologist and entrepreneur Howard Clifford in Detective Pikachu, he says, “you could have written what I knew about Pokémon on the head of a pin”. But his participation in the film demonstrates Pokémon’s mesmeric charm and curious pulling power: he fell in love and has now genuinely joined the Pokéfandom.

“I did a crash course in Pokémon lore and bought every book available, including the deeply impressive Pokédex,” says Nighy, referring to the Pokémon encyclopaedia. “I love the collecting. When I get around to it, I’m going to download the [Pokémon Go] app and go to Strasbourg. Someone told me they went Pokémon hunting in Strasbourg, which made an impression on me.”

Although he has since parted with his beloved Pokédex (donated to a small boy in Victoria, British Columbia), Nighy talks excitedly about a number of extremely rare Pokémon items, including a limited-edition Pikachu (“Pikachu, who can resist!?”) presented to him by the CEO of the Pokémon Company.

He has even brought hefty Pokémon pieces home to decorate his house. His character had a palatial office with “ancient Pokémon wall hangings, punched out in ancient stone, or at least given the appearance of that,” he says. “I now own them. They are absolutely enormous. They weigh a tonne. They’re in my cellar at the moment because I have to find a wall strong enough to hold them.”

Like most fans, Nighy also has his favourite Pokémon. “The ancient Mew was probably my top, top favourite because he’s just majestic and he was the very first ... He was elegant and powerful.”

Whenever a new generation of games comes out, it’s like a huge wave. I feel like the cycles go for two to three years Paul Franz, pokejungle.net

The creator of Pokémon is video game developer Satoshi Tajiri. His vision was simple: players would explore the fictional region of Kanto catching, training and battling 151 creatures called Pokémon, including the franchise mascot, Pikachu. The games had a heavy emphasis on collecting (Tajiri collected insects as a boy) and trading (it was impossible to catch them all without trading with a peer).

He pitched the game to Nintendo in 1990 and, six years of arduous development later, on 27 February 1996 Pokémon Red and Green were released in Japan for Nintendo’s handheld Game Boy system. When the games made their international debut as Pokémon Red and Blue in the autumn of 1998, it coincided with the launch of the trading cards, an animated series and a feature-length animated film.

Since then, the universe has expanded. Every new “generation” of Pokémon is marked by the release of a new video game and more creatures; the current total is 807 spanning seven generations. There are more than 100 additional video games, an animated series with more than 1,000 episodes, 21 feature-length films, 11,000-plus trading cards, and innumerable action figures, soft toys and comic books.

Pokémon fever has ebbed and flowed over the past two decades, but this year it is ratcheting up again. Pokémon Go, the phenomenally successful 2016 augmented-reality app that saw players risk their lives, was still the fourth highest-grossing mobile game in March 2019 (developers Niantic claim the app has been downloaded 850m times). While two games released last November, Let’s Go Pikachu and Let’s Go Eevee, have so far sold a combined 10.63m units. The next video game instalments – Pokémon Sword and Shield – are coming in November, ushering in the eighth generation. And fans cannot wait.

Joe Merrick of the fansite serebii.net

It is everywhere in pop culture too: there was a Pikachu party at Coachella last month and Jigglypuff-inspired clothes turned up on catwalks at Milan fashion week. The stars have also professed their love: Ariana Grande revealed a new tattoo of her favourite Pokémon, Eevee; Rachel Brosnahan told Jimmy Kimmel that she’s a Level 37 Pokémon Go master; and Queer Eye’s Tan France has taken to wearing Pikachu boots. It is fair to say that 2019 is shaping up to be the year of the Pikachu.

“Whenever a new generation of games comes out, it’s like a huge wave,” says Paul Franz, editor of Pokémon fansite pokejungle.net. “We’re having Sword and Shield later this year and the interest in the fandom is gonna be peaking for a little while. I feel like the cycles go for two to three years, so I think this is going to be a high point.”

“I’ve been joking for a while that 2019 is gonna be the new 2016, which was the new 1999,” says 32-year-old Joe Merrick, freelance writer and full-time webmaster of serebii.net, a website he started at 13, which he says is the biggest non-Wiki Pokémon fansite on the internet. Traffic to his website is as high as it has been since 2016, and Merrick feels this year could be the biggest ever for the franchise.

“There is a concerted effort to appeal to the original fans,” he says. “Nostalgia is definitely an element. You’ve got people in their late 20s and early 30s who loved Pokémon when they were growing up. They’ve now got kids and say: ‘I remember this, we should get our kids into it.’ That’s definitely a good marketing tactic.”

To tap into 90s nostalgia, the Pokémon Company has effectively “rebooted” the original 151 Pokémon and released a new line of Pokémon plush toys along with glossy remakes of the original games.

I'd love to have Pokémon as my job. My grandfather asked: ‘When are you gonna quit this thing?’ And I was like, ‘Never!' James Evans, world champion

The last big year, of course, was 2016, when Pokémon Go was released. Twenty-eight-year-old Marti Bennett, a freelance writer and Pokémon content creator on YouTube and Twitch, recalls the sudden excitement of everyone else joining in with her long-term passion. “I’d go into work and get five people bombarding me as soon as I entered the door: ‘Marti what’s all this Pokémon Go stuff about?’ [It was] the first time in the six years I’d worked there that they ever showed any interest.”

Almost overnight, the app’s staggering popularity made it inescapable in pop culture. It was the 90s all over again but with adults on iPhones rather than kids on Game Boys. Now a cutesy, childish universe felt mature and genuinely relevant. For 29-year-old YouTuber, Reversal, it was also a lucrative turning point. Reversal grew up playing the original games in the Netherlandsand grew out of them as a teen; then Pokémania hit him again with Pokémon Go. To say he takes Pokémon Go seriously is an understatement: he has travelled the world to try and catch them all (his next trip is to Singapore for an event called Safari Zone). He has registered having walked more than 4,500km on the app, caught 150,000-plus Pokémon and won upwards of 10,000 battles. When his friend spotted a nearby Girafarig – a Pokémon that had long eluded him – Reversal left his house immediately. It was 3am. “He texted me: ‘It’s here’,” says Reversal. “I went out and live-streamed it. I looked for it for about an hour.”

Before Pokémon Go, Reversal’s YouTube channel had more than 100,000 subscribers and he focused on mobile games such as Boom Beach and Clash Royale. When he turned to Pokémon Go, not everyone was thrilled. “I alienated the entire fan base,” he says. Yet soon, his audience had grown to three times its size. Reversal is guarded about money, but his channel has more than 337,000 subscribers and he says that he is much better off financially. His most-watched video – an eight-minute clip of him hatching rare Pokémon eggs – has 3.9m views.

But more traditional elements of the community are also attracting new, young fans. The competitive scene – where players battle with their virtual or trading card Pokémon – has flourished both locally and at the annual Pokémon World Championships (this year in Washington DC).

Sixteen-year-old Connor Pedersen, who is based in Sacramento, California, was the runner-up in the card game senior division finals last year. Before tournaments, he says he spends five hours a day practising with his cards (of which he lost count at 10,000). “I’ll do one marathon day where I’ll play 10 hours a day, like two weeks before the tournament,” he says.

Pedersen estimates he has made $30,000 in winnings so far, and plans to keep going for five years. But he says it’s not about the money. “I play it because I want to win the Worlds [Championships],” he says. “I’ve gotten so close so many times. There have been three years in a row where I’ve been in the top eight but I wasn’t able to win.” (He wants to be the very best, like no one ever was).

He is not the only one. James Evans, 15, from New Jersey, was the 2018 world champion for the video game senior division and has played in more than 50 tournaments worldwide. This year, like Pedersen, he has graduated to the masters division, where he competes at the highest level.

“I’ve been able to fight in a few major events and do pretty well in the first year,” he says. “Right now, my Pokémon career is going pretty well.” He estimates that practising and playing in tournaments takes up 40% of his time and – with the help of some very supportive parents – he travels all over the world competing (he’s been as far as Australia). Evans even has an arrangement with his school for additional time off, so long as he makes up the work.

“I would love to have this as my job,” he says. “I remember my grandfather asked me this question last year. He was like: ‘So when are you gonna quit this Pokémon thing?’ And I got really serious and was like, ‘Never!’”

Evans hopes the renewed interest in Pokémon this year will benefit the competitive scene. “Not only are we going to see a lot more people playing the game generally, but I think more people are going to gravitate towards playing competitively,” he says.

Among the Pokémon faithful there is a feeling of vindication. Los Angeles-based Sahagian has been a fan since the original games were released in the US. “When I go out and about in the world I’ll have some merchandise, like stickers on my car or a Pokémon backpack,” he says. “Pokémon just means so much to me. I’ve dedicated my life to bringing fans together to talk about it.”

Sahagian no longer feels alone. “We live in the age of Marvel movies being the top-grossing movies of all time; this is the age of the nerds now,” he says. “I think fans are much more willing now to show their excitement for the franchise. If they were hiding before, now they are more willing to be more open about their love.”

This article was amended on 9 May 2019. An earlier version referred to Marti Bennett and used the pronoun”his”. That should have been “her”.