Superman: Legacy has added the DC character of Metamorpho to the film's growing roster, and here is everything you need to know about the character's origins, Justice League connections, and place in the DCU. Since David Corenswet and Rachel Brosnahan were confirmed as Superman and Lois Lane respectively, the casting for Superman: Legacy has shifted into high gear. The most recent slew of casting announcements links to the pre-existing superheroes that will exist in Superman: Legacy alongside Corenswet's new take on the Man of Steel.
https://screenrant.com/who-is-metamorpho-justice-league-hero-explained/