Even though it's a sequel, it is entirely possible to see Godzilla: King of the Monsters without having seen its predecessor, Gareth Edwards' 2014 quasi-reboot, Godzilla. But if you really want to understand everything that happens in the new movie, you've got to watch not only Edwards' dark spectacle, but up to a dozen other movies in the franchise's long, rich history as well.
Since the massive radioactive beast first emerged from the sea to decimate Tokyo in 1954, there have been well over 30 movies featuring Godzilla, including 29 live-action flicks produced by Toho, the legendary Japanese studio. Director Michael Dougherty, a lifelong fan, borrows from and alludes to this rich history in liberal doses in Godzilla: King of the Monsters, with some of the older movies providing major plot points and others identifiable only with passing references. When SYFY WIRE spoke with Dougherty about Godzilla: King of the Monsters and its references last week, he teased a few movies that fans would do well to have seen ahead of watching his movie.
**Spoiler Alert: There are very, very light spoilers for Godzilla: King of the Monsters below**
Along with the original Godzilla and the American re-working that came out two years later (the similarly titled Godzilla, King of the Monsters!), Dougherty named Ghidorah, The Three-Headed Monster (1964) as a heavy inspiration, because it was the first time that Godzilla was joined on screen by Mothra and King Ghidorah, two of the three other classic Toho monsters who appear in the new movie. Those movies feature a plethora of items that get name-checked or referenced in Godzilla: King of the Monsters.
It would help fans to also see Mothra (1961) and Mothra vs. Godzilla (1964). The first introduces Mothra and provides crucial background information that comes into play late in Godzilla: King of the Monsters, while the latter marks a major turning point in the franchise. Invasion of Astro-Monster (1965), the second Ghidorah movie, is also crucial.
(It should be noted here that unlike many franchises, the Godzilla movies were never concerned with keeping up continuity. Toho has made three distinct eras of monster movies, beginning with Showa [1950s-'70s] and then Heisei ['80s-'90s] and Millennium [1999-2000s]. Most monsters have several different origin stories, even within each era. That's part of why there are so many movies worth watching ahead of Godzilla: King of the Monsters.)
Meanwhile, the 1992 movie Godzilla vs. Mothra (they just switched the names around) was one of several to feature ancient cave paintings that offer some explanation of the monsters' origins. The 2001 flick Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack positions several of the monsters as Earth's ancient guardians, which tracks with Dougherty's new movie as well.
The global monster rampages teased in the previews for the new movie hearken back to Destroy All Monsters (1968), which was sort of the Avengers of Toho monster movies at the time, as it set many different kaiju free to romp through different cities and then brought them all together. The spirit of that movie was recreated in 2004's Godzilla: Final Wars, which makes it worthy of checking out as well.
The movie that came after Destroy All Monsters was a clip-heavy flick called All Monsters Attack (1969). It is the only one that stars a child, which makes it quite relevant to King of the Monsters, which focuses on a character played by Millie Bobby Brown. It also features Mothra's powder providing magical effects for a fellow kaiju, though we won't say more.
We won't give away why you should watch them, because they're referenced in the final battle, but Godzilla vs. Mechagodzilla II (1991) and Godzilla vs. Destroyah (1995) are also recommended viewing.
Rodan is the final giant name-brand Toho monster being introduced in King of the Monsters, and most of its appearances are covered in the movies listed above. That said, you'll also want to watch Rodan (1956), which introduces the character and gives a lot of background information that'll help you better understand that giant flaming bird.
There are likely even more references to other movies — Daugherty packed in things like the presence of a weapon called a Maser, which was seen first in the Toho film War of the Gargantuas and then throughout different Godzilla and kaiju movies, so it'll take many views to decode them all. But this list should get you in pretty great shape for your first screening.