The initial scene often creates a small, self-contained story that anticipates the theme, structure, or individual events of the larger storyline (Raiders of the Lost Ark). The protagonist of the initial scene is not necessarily the protagonist of the story that follows: Trinity in The Matrix, R2D2 and C3PO in Star Wars (4).
Recent films, influenced by modern TV conventions, often use the opening scene to create a mystery or question that is resolved later in the story (Black Panther has two introductory scenes — one a mystery in the past and the other a more conventional preparation scene in the present, plus a preliminary spoken exposition, similar to the title crawl in the original Star Wars).