A planet in the same solar system as Earth, within the mythology of the Flash Gordon serials it is a world with a breathable atmosphere, and with a gravity and temperature favorable to supporting human life. The inhabitants all speak American English.
Though Mars is nominally ruled by Queen Azura, it is populated by distinct factions, not all of whom are necessarily loyal to the monarch.
Elsewhere lies the Forest Kingdom, whose inhabitants the Forest People possess the black sapphire and are thus protected from Azura's magic power.
The primary means of transportation on Mars is the Stratosled. Vacuum Cars allow for high-speed transportation of limited numbers of people. Long-range communication is achieved by means of a Televisor. The more primitive Forest People use Signal Trees.
Earth existed in peaceful ignorance of Martian life until it was subjected to an unprovoked attack by means of a devastating Nitron beam set up by Queen Azura following her alliance with the former ruler of Mongo, Ming the Merciless. This led to 2 separate bids to terminate this attack. First, a party from Earth itself, led by Flash Gordon, Dr. Hans Zarkov, Dale Arden, and Happy Hapgood. Second, by Prince Barin of Mongo. This precipitated a series of events which led to the death of Queen Azura, after which Mars came under the more benign rule of the Clay King, with Prince Barin taking a temporary leadership of the Forest People in an attempt to reconcile the opposing factions.