P3X-421 is a planet in the Milky Way galaxy of a primitive human people who previously worshiped the Goa'uld. After the Goa'uld were defeated by the Replicators, Stargate Command sent Dr. Lindsay to aid the people. The planet was also visited by an Ori Prior who came to preach about Origin. He was taken from the planet by SG-12. (SG1: "Origin")