Monster Zero is a fictional code designation featured in the Godzilla film series of the Shōwa period. They appeared in the 1965 film Godzilla vs. Monster Zero (also known as Invasion of Astro-Monster). Used by the alien race known as Xians, it referred to any of three different giant monsters.
- Monster Zero, Referred to King Ghidorah.
- Monster Zero-One, Referred to Godzilla.
- Monster Zero-Two, Referred to Rodan.