Clark Kent is Superman's civilian identity. He adopts this name to blend in with humanity and protect his loved ones.
The film focuses on Superman's origins and his struggle to reconcile his alien heritage with his human upbringing. He lives as Clark Kent, working as a journalist, but his true identity as Superman becomes increasingly public as the film progresses.
Therefore, there's only one character, Superman/Clark Kent, who is both the alien superhero and the human journalist.