Mongo is a rogue planet that travels through our solar system under the control of its dictator, Emperor Ming. Mongo is an inhospitable planet, with various extreme climate zones. Travelers to Mongo must pass through a "Death Zone" on the way, described by scientist Dr. Hans Zarkov as being "a zone devoid of any force". 
Mongo has at least two recognised moons, one of them being the planetoid Lunita.
The area around the Emperor's palace is desolate and devoid of vegetation. Giant dragons live in the nearby caves. Other vicious animals of Mongo include monkey men, orangopoids and white-striped, bear-like animals.
The people of Mongo have progressed scientifically beyond Earth. According to Ming, "the reason for our success is that we possess none of the human traits of kindness, mercy or pity! We are coldly scientific and ruthless!" 
A description of the fictional planet Mongo states: "Mongo is approximately one of the diameter of earth but has a gravitational density that is only slightly less. It is a relatively young world with towering mountains not yet worn smooth by time and many areas of volcanic activity. Its vegetation is still limited to isolated areas of botanical giants. Biologically it is still in the era of reptilian giants. Man evolved fast into diverse races, many of which possess amazingly advanced technology while others still live in primitive and unexplored regions." It is divided in several realms and the major ones are:
- Arboria is a forest principality with Prince Barin as the governor,
- Frigia is a frozen kingdom, and the ruler is Barin's cousin, Queen Fria,
- Coralia is an underwater kingdom beneath the Sea of Mystery. It is located east of Arboria and is ruled by Queen Undina,
- The Land of the Lion Men also borders the Sea of Mystery, and is ruled by King Jugrid and Prince Thun,
- The Magnetic Mountains are located east of the Land of the Lion Men and is a base of operations for Ming, the ousted king of Mongo,
- The Sky City of the Hawk Men is located north of the Magnetic Mountains, and the leader of this realm is King Vultan,
- Tropica is a continent of forests. It is directly east of the Sky City. Queen Desira rules Tropica.
- The Fire Lands are located on the east coast of Tropica, and is home of Gundar, the Desert Hawk.
- ↑ Flash Gordon (1936), "The Planet of Peril".
- ↑ Flash Gordon comic strip. February 11, 1934.
- ↑ "The Outlaws of Mongo", December 12, 1937.
- ↑ Map of the Planet Mongo
- ↑ Flash Gordon’s planet Mongo