Space Western is a subgenre of science fiction that uses the themes and tropes of Westerns within science-fiction stories in an outer space setting. Subtle influences may include exploration of new, lawless frontiers, while more overt influences may feature literal cowboys in outer space who use rayguns and ride robotic horses. Although initially popular, a strong backlash against perceived hack writing caused the genre to become a subtler influence until the 1980s, when it regained popularity. A further critical reappraisal occurred during the 2000s due to critical acclaim for Firefly. Source: Wikipedia (en)