In 1993, way before most members of current gonzo rap collective Odd Future could even walk, New York City's Wu-Tang Clan were busy reinventing hip-hop. At the time, the genre was dominated by west-coast rappers and G-funk, with Dr Dre and Warren G creating hypnotic, synth-heavy summer anthems that usually involved someone driving a convertible that "bounced" in the video. By November of that year, Wu-Tang Clan's classic debut album, Enter the Wu-Tang (36 Chambers), had cast a long shadow with its lyrical wordplay referencing everything from martial arts movies to darkly humorous threats of violence. They were in complete contrast to what was popular, with classic soul samples eerily interwoven with aggressive, gritty beats and early press shots featuring all nine members hidden behind makeshift masks. If Odd Future have recently caused a minor sensation with their playground antics, then Wu-Tang Clan pretty much tore up the rap rule book and smoked it.

Central to Wu-Tang Clan's success form the start was Robert Fitzgerald Diggs, aka RZA. Initially going by the moniker Prince Rakeem, Diggs changed it to RZA (or Ruler Zig-Zag-Zig Allah) in 1992 when he and his cousins Ol' Dirty Bastard and GZA, along with six other rappers, formed the group in Staten Island. As well as producing the majority of the Wu-Tang output (including various solo albums), RZA was also the de facto leader, outlining early not only his commitment to the group but also his business mind by creating a "five-year plan", which stated that as long as he had total control, Wu-Tang Clan would dominate hip-hop within five years. When 1997's Wu-Tang Forever knocked the Spice Girls off the No 1 slot in America, selling more than 600,000 copies in a week, RZA was true to his word, handing over all aspects of the Wu-Tang franchise (which by this point included a successful clothing line, Wu-Wear) to his associates.

It's around RZA that Wu-Tang Clan orbits. It's his idea of them being more of a family than a group that means when he goes off to act or write film scores (as he has done for Quentin Tarantino's Kill Bill and Jim Jarmusch's Ghost Dog), it's understood that he'll always return. It means it's no great surprise to hear he won't be joining the rest of the group for their current European tour. "I'm in the middle of editing a movie right now and I'm not allowed to leave California due to contractual agreements," he says. RZA wants the film, The Man with the Iron Fist – his directorial debut and produced by Tarantino – to show "the creativity of hip-hop artists". "I've always wanted to show the world that hip-hop artists aren't limited to the bubble we was put in, you know, just a bunch of guys rapping about drugs and streets and things like that," he explains. "I took time to educate myself in many fields of creativity and technology as well as honing my skills as a human being."

The film is clearly important to him, but so is Glastonbury, and a deal has been struck for him to join the rest of Wu-Tang Clan for that weekend only. "I'm doing that one more for the charitable cause of it and I got my producer to slip me out for that one," he laughs. "I'm very aware of what Bono does; I spent some time with him some years ago and he's always given to a worthy cause and I know he's going to be part of it. I just love when artists come together for a cause other than collecting our fees." It's also about continuing where Jay-Z left off at Glastonbury two years ago and helping send out the right message about hip-hop. "Jay-Z is in the same ideology that Wu-Tang is in, you know what I mean, guys that started from the bottom, that understand how it is to be at the bottom and make it to the top. There are many people who are still at the bottom and we're trying to give back."

Perhaps it's the alignment with Jay-Z, or working on the last Kanye West album, or the rise of Odd Future ("I haven't heard their music yet, just been hearing their name so I'm going to research the music and see what level they're on."), but RZA seems energised by the influence he and Wu-Tang Clan have had. But he's still learning. Talking about collaborating with West, he refers to his work ethic, comparing him to a movie company that works to a tight schedule, never just rolling into the studio at midnight. A conversation about an aborted collaboration with Björk in the late-90s brings about a revealing admission. "I kind of was like just having fun, getting high, making music and not looking at the big picture of what my music was doing," he explains. "I didn't travel a lot and I didn't understand the power of my music until the last 10 years when I really realised who I was and what I meant to the world as a musician. Before, I was just an egotistical maniac – thought I was the best rapper, producer in the world and then realised that it took a lot more to be a good musician, to be a good artist."

It's this desire to cement his legacy that's not only seen him return to his other group, Gravediggaz – a horrorcore rap collective who are currently working on a new album, tentatively called Return of the Niggamortis – but also bring the late Ol' Dirty Bastard's son Boy Jones into the Wu-Tang fold. "He's an embodiment of his father, and I mean literally. When you see this kid he looks like his father, he acts like his father and this is without drinking or smoking, you know what I mean," he laughs. "It's not drug-induced, it's natural. He actually proved a theory to me – I always thought that some of Dirty's personality came from substances, but no, it's in his genes, in his blood – and his son is an example of it." In fact, Jones represents the second generation of Wu-Tang. "I hope that he has a good future in hip-hop and he can carry on the Wu-Tang legacy because he's kind of the first-born son of the Wu-Tang. Oldest child out of all the children. I think he'll be the first one to come into the world and show the next generation of Wu-Tang talent."

As well as the Glastonbury performance, there's also a new Wu-Tang EP in the works and a compilation album, Legendary Weapons, due in June. RZA now seems as caught up in the Wu-Tang world as he ever was. Talking about the Gravediggaz reunion, he could also be talking about Wu-Tang Clan when he says: "Hip-hop is almost gone, we might as well go back and recreate it, and why not me recreate it seeing as I'm the father of it?" At the end of our conversation, in lieu of a goodbye, he says "Wu-Tang for ever" – and you totally believe him.

• Wu-Tang Clan play the London HMV Forum (12 June), Birmingham HMV Institute (13 June), Edinburgh HMV Picture House (14 June), Manchester Academy 1 (15 June) and the Glastonbury festival (25 June).