Space Western is a subgenre of science fiction which uses the themes and tropes of Westerns within science fiction stories. Subtle influences may include exploration of new, lawless frontiers, while more overt influences may feature literal cowboys in outer space who use ray guns and ride robotic horses. Although initially popular, a strong backlash against perceived hack writing caused the genre to become a more subtle influence until the 1980s, when it regained popularity. A further critical reappraisal occurred in the 2000s with Firefly.