Joss Whedon believes that Henry Cavill is the best actor to play Superman since the most iconic and popular Superman, Christopher Reeve. Reeve first played the Man of Steel in 1978's Superman, which was directed by Richard Donner. Reeve's portrayal combined with Donner's direction helped define Superman for decades with Clark Kent/Superman becoming the starring role of Reeve's career. Some of this is due to a tragic horse riding accident that left Reeve a quadriplegic shortly after his last Superman appearance. More of it, though, is due to the popularity and appreciation that fans have had for Reeve's portrayal.
Reeve's interpretation of Superman is so popular that it arguably set the standard for all other Superman roles to follow. After all the Superman actors that followed Revee, Brandon Routh in Superman Returns, was based directly on his predecessor and was even set in the same continuity. However according to the man who most recently directed the current Superman Henry Cavill, the British actor has everything and more needed to be the Man of Tomorrow.
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Whedon weighed in on Cavill's worth as Superman on his Twitter account. This is after a fan lamented the uncertainty of Cavill's future as Superman and how it's unlikely fans will ever see Cavill in a Superman movie that has the same optimism as the Reeve/Donner era. Whedon responded by asserting that Cavill is a great Superman. In Whedon's opinion Cavill could even surpass Reeve if he received the right material or barber (which seems to be a not-so-subtle dig at Cavill's CGI-removed mustache in Justice League).
It's a bit strange for Whedon to be ribbing the material that Cavill's Superman has received so far even if it's in a harmless manner. This is because Whedon partially directed and wrote 2017's Justice League. Granted, Justice League is a project that Whedon inherited from the previous Superman director Zack Snyder. Snyder cast Cavill as Superman and worked with him on Man of Steel and Batman v. Superman and is consequently responsible for the bulk of Cavill's Superman direction. However, it's been rumored that Whedon was responsible for re-shooting and changing most, if not all, of Snyder's Superman material in Justice League.
Ignoring Whedon's complicated history with Cavill's Superman, his opinion is probably one that a great number of fans share. While the films that Cavill has appeared in as Superman have not been warmly received as a whole, Cavill's performance has been a consistent point of praise. Sadly, DC and Warner Bros' future with Cavill's Superman is very much in a state of flux. There were reports that Cavill had left the role but those were later disputed by the actor. Regardless if Cavill technically still has the role, Warner Bros. is moving away from Superman as the face of the movie franchise. Instead they're pivoting to other superheroes like Wonder Woman and Aquaman.
Currently, Whedon has very little known involvement in DC and Warner Bros' movie plans. Shortly before he directed Justice League Whedon was attached to a Batgirl film but has since left the project altogether. It's therefore unlikely that Whedon's opinion holds much clout in the process of another Superman movie getting made with Cavill in the lead role. It's nevertheless interesting that Whedon, who is responsible for Cavill's latest and least successful portrayal of Superman (at least in terms of box office intake), wants to see the actor get another shot.
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Source: Joss Whedon