Actor and producer Vin Diesel, the star and arguably the creative mastermind of the Fast & Furious franchise, is a big Dungeons & Dragons fan. When promoting Furious 7 in 2015, the actor actually played a full game with folks from the site Nerdist, both to show off his role-playing chops and to symbolically bridge the gap between high school cliques, telling the nerds that it was okay to love his movie franchise seemingly geared at motorheads.

Diesel’s D&D love is a window into why the Fast & Furious franchise (or the Fast Saga, as the poster for F9, the latest installment in the series, would have it) has become so beloved by so many different people. It’s also a window into Diesel’s canny knack for knowing exactly what people want to see from him (and his movies), and why.

More than anything else, it’s a window into just how this franchise went from being about illegal street racers tearing up the streets of Los Angeles to one where a secretive CIA operative named Mr. Nobody sends a desperate cry for help to international super-spy Dominic Toretto (Diesel) when his plane crashes in a Mexican jungle, as happens at the beginning of F9. The expansion of the characters’ powers and the inflation of the films’ dramatic stakes seem ludicrous from the outside but completely believable if you watch all nine films in a row. (A 10th film, 2019’s Fast & Furious Presents: Hobbs & Shaw, exists, but this spinoff really isn’t a key part of the core storyline.)

Why does it work at all? Well, look at D&D. In the classic role-playing game, characters are supposed to continually level up. In a traditional campaign (a story that unfolds over many sessions and often many years), the heroes start off facing low-level monsters and criminals threatening their tiny village, but as their powers grow, they tackle more existential threats, like enormous dragons or sorcerers who threaten to end the world.

In any good D&D campaign, the core characters grow and change together. Their bonds become solid and even unshakable, no matter what strife they face. The story is as much about the ways they become an ad hoc family as it is the bigger, badder monsters they face off against.

Am I saying the Fast & Furious franchise is a really good D&D campaign where the stakes keep rising higher and higher because they have nowhere else to go? I’m not not saying that.

With each successive film, Fast & Furious becomes a little more ludicrous and a little more irresistible — and the world has embraced that idea. The eighth film, 2017’s The Fate of the Furious, made $1.2 billion at the global box office, less than 2015’s Furious 7 ($1.5 billion) but well above 2001’s The Fast and the Furious ($206 million). This is, give or take a Marvel Cinematic Universe, the most significant movie franchise going right now.

Now, with F9 entering theaters as one of the presumed titans of the summer box office, at a time when many of us are finally comfortable returning to movie theaters, it seems clearer than ever that this goofy, over-the-top film franchise with a heart of gold is the film franchise of the moment. We don’t know what 2021 will bring — but we at least know that any problem faced in the Fast & Furious universe can be solved by throwing more cars at it.

With all of that in mind, here are three major themes that have made the Fast & Furious franchise so memorable and so lucrative.

Theme 1: Franchise

Part of the fun of following the Fast & Furious franchise is getting wrapped up in the meta-narrative of its existence as a franchise — its long, strange path through the multiplex, across 20 years. To watch any given movie is to see an almost perfect time capsule of that point in both franchise history and in film history. As Hollywood moviemaking got bigger and sillier, the Fast & Furious movies did so at almost exactly the same rate.

In so many ways, the most significant film in the Fast & Furious series is the one that seems to have the least to do with the core storyline. 2006’s The Fast and the Furious: Tokyo Drift is the third installment in the franchise, and it ditched all the characters from the first two films in favor of a story about an American teenager moving to Tokyo and learning how to drift race — wherein a car seems to float around a curve, almost perpendicular to it. (The movie takes great pains to explain the mechanics of drift racing but could have just said, “It’s cool to watch, huh?”)

Tokyo Drift completes the first trilogy of Fast & Furious movies, but those first three films are largely disconnected from one another — they’re mostly about cars going really fast and the daring people who drive those fast cars. There’s a loose overlay of drivers doing crimes — and breaking up crimes — but they attempt to maintain a vague tether to reality. The first two films center on undercover cop Brian (played by Paul Walker, who died in 2013), who uses his sweet driving skills to ingratiate himself to various folks law enforcement wants to keep an eye on, notably Dominic Toretto (Diesel). Diesel’s star power basically hijacks and runs away with 2001’s The Fast and the Furious, the first movie, and when he refused to return for 2003’s 2 Fast 2 Furious, the sequel was reconfigured to follow Walker’s Brian as he solves crimes by driving really fast in Miami.

Tokyo Drift featured neither Dom nor Brian. It didn’t feature Dom’s love interest Letty (Michelle Rodriguez) or Dom’s sister (and later Brian’s wife) Mia (Jordana Brewster), or any of the new characters Brian met in 2 Fast. The movie’s all-new ensemble made it easy to imagine a long series of diminishing returns for Fast & Furious, if the franchise continued at all. Tokyo Drift remains its box office nadir, so everything petering out after that film was a distinct possibility. An endless series of cheap sequels set around the globe, with casts of inexpensive actors and some cool car stunts, was completely plausible.

Instead, Dominic Toretto returned in Tokyo Drift’s last few minutes, and the franchise’s history changed completely.

Diesel didn’t particularly long to return to Fast & Furious, but Universal, the studio behind the franchise, persuaded him to come back by offering him the rights to a franchise he did want — Riddick, a series of cult sci-fi movies where Diesel plays a big bruiser of an action hero in space. Diesel agreed, and his short cameo at the end of Tokyo Drift accidentally established that even if the first three movies shared few characters, they took place in a larger universe of daring street racers pulling off impossible feats.