9. Reggie Mantle - Riverdale
Ross Butler portrayed Archie Comics character Reggie Mantle in a recurring capacity throughout Riverdale's first season, but when the character's role was increased in the second, he was unable to return due to the fact that he had a much more significant role on Netflix's 13 Reasons Why (in which he portrays Zach Dempsey)
As a result, the role was recast with Charles Melton stepping into Reggie's shoes in a series regular position. Since then, the character has gone on to become a huge part of the show and, in spite of a number of head-scratching storylines, Melton has done a great job bringing him to life.