Two characters in Marvel's Cinematic Universe have just been upgraded to recurring status even though the film in which they first appear -- "Guardians of the Galaxy Vol. 2" -- has yet to be released. One of those characters is the larger-than-life Ego the Living Planet, played by Kurt Russell, while the other is yet-named, but confirmed to be played by veteran action movie star Sylvester Stallone.

Director James Gunn recently sat down with Fandango to talk about "Guardians Vol. 2" and how Russell and Stallone's characters are pivotal to both the film's story and Marvel's overarching, multi-film narrative.

"This is definitely not a one-off [for them]," Gunn said. "They’re both characters that we’ve taken a lot of time to develop, and they’re a big part of the MCU now."

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Marvel's Cinematic Universe is currently in its third phase, which has gradually pivoted to focus on both the magical and cosmic aspects of the comic book company's expansive lore, as seen in "Doctor Strange" and the first "Guardians" film. The cosmic trend looks to continue with the 2018 film "Thor: Ragnarok," which strands Chris Hemsworth's Thor on a hostile alien world, and is followed shortly after by the two-part "Avengers: Infinity War" arc that focuses on the mad titan Thanos' bid for universal power and destruction.

It's unclear how deeply Ego the Living Planet or Stallone's character will be embedded in these narratives, but with the Avengers and crew shipping off for worlds unknown, there's a decent chance such mighty galactic and cinematic forces are liable to reappear down the road. A character like Ego, after all, has existed in the Marvel canon for just over 50 years.

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Ego originally debuted in "Thor" #132 as an antagonist who is consuming spaceships and other planets to sustain himself, with the eventual aim of interstellar conquest. Thor shows Ego the error of his ways and from that point forward the planet-sized creature is largely considered neutral, though is often driven to violent outbursts resulting from temporary insanity.

Debuting in theaters on May 5, "Guardians of the Galaxy Vol. 2" is a production of Marvel Studios directed by James Gunn and starring Chris Pratt as Star-Lord, Vin Diesel as Baby Groot, Zoe Saldana as Gamora, Bradley Cooper as Rocket Raccoon, Dave Bautista as Drax, Michael Rooker as Yondu, Elizabeth Debicki as Ayesha, Chris Sullivan as Taserface, Kurt Russell as Ego the Living Planet and Sylvester Stallone.