Earth-X was a parallel Earth in the Pre-Crisis Multiverse, on which World War II never ended. American President Franklin Delano Roosevelt passed away from a cerebral hemorrhage in 1944, leaving the country in such a state that Nazi Germany was able to develop atomic weaponry. By this point, both countries were reluctant to use such destructive capabilities against the other for fear of retaliation that the conflict continued using conventional warfare. Adolf Hitler's Nazi war machine soon reached American shores and dominated the country. American soldiers tried to fight back, but by this point Hitler had developed mind control technology that weakened the opposition's willpower. By the early 1970s, the flag of the Third Reich flew across the entire nation. Some proved to be immune to the effects of the mind control devices, and small resistance pockets began to form in various cities.
Japan was originally an ally of the Nazis, but, when they seemed to have won the war and laid down their arms, the Nazis betrayed them. 
The Freedom Fighters, originally from Earth-Two, migrated to Earth-X to continue the fight for freedom from Nazi oppression. In 1973, members of the Justice League of America from Earth-One and the Justice Society of America from Earth-Two arrived on Earth-X by way of a Transmatter Cube accident. They paired off with various members of the Freedom Fighters and helped them fight the Nazi threat.
- Martha Roberts (Deceased)
- Professor Roberts (Deceased)
- Captain Triumph
- Invisible Hood (Deceased)
- Magno (Deceased)
- Neon the Unknown (Deceased)
- Plastic Man (Deceased)
- Red Bee (Deceased)
- Red Torpedo (Deceased)
- Blackhawk Squadron (Deceased)
- The continuity of Earth-X has been retroactively allocated to the realities presented in titles published by Quality Comics.
- In the post-Infinite Crisis Multiverse, Earth-10 is based on Earth-X (X being the Roman Numeral for 10).
- In Earth-X continuity, President Franklin Delano Roosevelt had a heart-attack and died in 1944. In all other realities, Roosevelt passed away in April of 1945.
- According to the Official Crisis on Infinite Earths Cross-Over Index, the Quality characters, before the DC revamping event called "Crisis on Infinite Earths", existed on two separate realities in the DC Multiverse: Earth-Quality and Earth-X. While Earth-Quality followed much the same history as the main Earths, Earth-X was radically different in that World War II continued there until the 1980s, enabling the Freedom Fighters to continue their fight against the Nazis.
- Characters from Earth-X
- Other things related to Earth-X
- Earth-X's Comic Appearances
- Reality Gallery: Earth-X