It's a movie that received a fair amount of acclaim but Stephen Merchant's Caliban might be one of the most underrated elements of Logan. Hugh Jackman was far from the first choice for Wolverine in 2000's X-Men, with Russell Crowe passing on the part and Dougray Scott having to drop out due to schedule issues with Mission: Impossible II. Fans hated his casting too, feeling he was too tall, but the role proved to be a star-making for Jackman.
Hugh Jackman would reprise the part for a further eight movies, including cameo appearances, in addition to proving the voice for numerous video games. Logan would prove to be his final time donning the claws, but instead of a glossy comic book adventure, the movie was a brooding, R-rated character study. It took place in a world where mutants had been essentially wiped out, with a weathered Logan looking after a sick Professor X (Patrick Stewart, Charlie's Angels); once he learns he has a clone/daughter called Laura (Dafne Keen), his quiet existence gets messy.
Logan director James Mangold previously directed The Wolverine which saw the title character travel to Japan. The movie was intended to be a character piece too but its blockbuster budget demanded it feature big action setpieces and mutant villains too. This resulted in an overblown finale where Wolverine fights the Silver Samurai, which is cited as the weakest part of the film. This is why Mangold insisted on making a more mature follow-up that stripped most of those elements away, which is reflected in the characters of Logan, Professor X, and Caliban.
Caliban had previously appeared in X-Men: Apocalypse played by Tómas Lemarquis (Snowpiercer), but that version seems to have little to do with Logan's take. In Mangold's film, he's played by Stephen Merchant, co-creator of The Office UK and as an actor is best known for comic roles. Caliban is a complete departure, with the character being an albino mutant who has gone into hiding with Logan and looks after Professor X. The relationship with Logan is like an unhappy marriage and one borne out of necessity.
Like the comics, Caliban's gift is the ability to find other mutants, which he used to help Logan's villains before fleeing when he learned what they were doing. The Caliban of Logan is run down by the time the movie begins, with Merchant brings a touching humanity that also helps set the movie's grounded tone. He's one of the last remaining mutants and is eventually forced to once again help the bad guys, lead by Donald Pierce (Boyd Holbrook, The Predator) track down Logan and his daughter. He later sacrifices himself using grenades to blow up a truck, in a sequence that was already emotional thanks to the death of another key character.
Logan received acclaim for its performances, mature themes and even earned a Best Adapted Screenplay nomination at the Academy Awards. Stephan Merchant's naturalistic, haunted Caliban tends to get overlooked when the praise is being handed out, but its a great performance that deserves a little more attention.