Sequels, series, serials, and remakes are evidence of the commercial imperatives governing most forms of cinema. Producers, directors, and writers have often been under pressure to recycle popular formats, formulas, and themes as a way to minimize risk and ensure profitability. Sequels, series, and remakes also reflect the tendency of most forms of entertainment and art to engage in repetition or variations on a theme. Artistic patterns can be found in all genres: trilogies, suites, triptychs, canons, rhyme schemes, and motifs, to name a few, all point to the repetitious core at the heart of most aesthetic phenomena. Yet even as sequels, series, and remakes overlap, they also establish their own individual characteristics. The Superman character, for instance, has gone through numerous incarnations, including the 1978 film Superman (1978), a remake of two Columbia serials (based on comic strip characters created by Jerry Siegel and Joe Schuster) that gave rise to a sequel, Superman II (1980), and to two more films in a series of four.