For a while, it was conventional wisdom: Hollywood had lost the ability to make new movie stars. The cultural machinery that once turned actors into icons was broken and seemingly unfixable. Studios had given up on the medium-budget character-driven films that produced the A-listers of previous generations. Instead, they bet the farm on sequels, superheroes, and other franchise IP, which were easier to market but stifling to the humans wearing the unitards. Marvel...