‘The Kings’ crafts a royal docuseries around Sugar Ray Leonard and his boxing peers

“The Kings” is ostensibly about four great boxers who reigned supreme via a series of epic fights in the 1980s, picking up the sport’s mantle from Muhammad Ali. But the filmmakers have ambitiously reached — and at times overreached — to transform that rich backdrop into a referendum on a changing America, devoting ample time to the Reagan years to complement the fireworks in the ring.

Give this four-part Showtime docuseries points for the effort, although like any good sports metaphor, the analogies about greed and “morning in America” only go so far. What’s left, fortunately, is a frequently fascinating look at these larger-than-life personalities — who join in the reminiscing, heard but not seen — whose reputations benefited from competing with each other.

Inevitably, the spotlight keeps swinging back to Sugar Ray Leonard, the wildly telegenic Olympic champion whose buoyant persona and good looks made him Ali’s natural heir. Yet he had to not only claw his way to the top but also face three other for-the-ages fighters to stay there: Roberto (“Hands of Stone”) Duran, Marvelous Marvin Hagler (who died in March) and Thomas “The Hitman” Hearns.

Leonard’s media savvy, endorsements and lucrative paydays provoked envy among his peers, but also made him an extremely inviting opponent. Yet when Leonard wasn’t available — including several retirements and eventual comebacks — the other three waged memorable brawls, moving up and down in weight classes and producing classic fights that come flooding back watching the well-curated clips.

Showtime boxing analyst Steve Farhood calls that stretch “maybe the greatest period in the history of the sport,” highlighted by the unforgettable Leonard-Duran bouts in 1980, which ushered in what would become the quartet’s decade.

Among the juicy tidbits Duran recalls taunting Leonard’s wife to lure him into a toe-to-toe slugfest in their first contest, and how he was weakened for the rematch — with its infamous “No más” ending — by having to drop 50 pounds in order to make the qualifying weight.

“He got inside my head,” Leonard says regarding the fight that he lost before humiliating Duran in their next encounter. “He got under my skin.”

Beyond the transition from the Carter to Reagan administrations, “The Kings” takes a detour into relations between the US and Duran’s native Panama, which fueled a hostility toward America that motivated him.

There is also a sobering aspect to the brutality of boxing, and the evidence of the toll years of blows exact on fighters. Analysts talk of these boxers being “addicted” to the thrills, money and competition, in almost every case (Hagler being an exception) hanging on until well past their primes.

In terms of boxing history, “The Kings” makes a compelling case that Leonard, Duran, Hagler and Hearns — who managed to shift the spotlight away from the heavyweight division — bridged the gap between Ali and the arrival of Mike Tyson, the subject of a recent ABC documentary. (Ali’s legacy is also featured “City of Ali,” a new documentary about his death’s impact on his home town of Louisville.)

The interviews also underscore the camaraderie that finally emerged among these men, who stalked each other outside the ring — seeking that next big payday — as aggressively as they battled inside it.

“Only they understand what they’ve been through,” trainer Teddy Atlas says.

“The Kings” gets a little carried away with the political and cultural overtones of that, but by the time the final bell rings, viewers will understand this generation of boxing royalty better too.

“The Kings” premieres June 6 at 8 p.m. ET on Showtime.