Based on the characters created by Stan Lee and Jack Kirby in Marvel Comics, "X-Men", directed by Bryan Singer, was released in 2000, and its success led to a series of sequels, prequels, and spin-offs, with the popularity of the series seeing a re-emergence of the superhero genre.
McKellen, who played the magnetic Magneto in the films, shared a picture on Twitter where he could be seen making a call from a "working phone booth" with the date of the film's release visible on a large hoarding.
"It was twenty years ago today, when there was still a working phone booth on Santa Monica Blvd and La Brea," he captioned the photo.
Jackman, who shot to international fame as the adamantium-clawed mutant Wolverine in his first Hollywood film "X-Men", shared an old video from his initial training days fighting a Wolverine figurine.
"So here's the thing. When the studio asked if I could be in shape to play #wolverine in 3 weeks ... I might (have) over promised. But wouldn't you have too? Happy Anniversary X-Men universe. #xmen," the actor said.
Jackman holds the Guinness World Record for "longest career as a live-action Marvel superhero" for playing Wolverine. He has played the character in eight films in the franchise, while fronting "X-Men Origins: Wolverine", "The Wolverine", and "Logan", his swansong as the mutant in 2017.
Berry, who starred as the weather mutant Storm, shared a cartoon of herself with cast members as their characters - Wolverine, Jean Grey, played by Famke Janssen, and Cyclops, essayed by James Marsden.
"#XMen20thAnniversary," she captioned the picture on her Instagram Story.
Janssen shared the poster of the film on Instagram and wrote "Happy 20th Anniversary to X-Men the Movie".
The original film also starred Patrick Stewart as Professor X, the founder of X-Men group, Rebecca Romijn as Mystique, Anna Paquin as Rogue, Ray Park as Toad, Tyler Mane as Sabretooth, among others.
The upcoming "The New Mutants" will be the 13th and concluding film in the series, after Disney inherited the film upon acquiring 20th Century Fox. RDS BK BK