The New Adventures of Flash Gordon (1979) Complete Archive Collection

The animated series' first season follows, more or less, the traditional Flash Gordon mythos, opening with the launch of the rocketship carrying Flash, Dale Arden, and Dr. Zarkov from somewhere in the Eastern Hemisphere (or at least the opening scene shows the ship clearing Earth's atmosphere above Europe and the Middle East). The series actually opens with the crash of the Terran ship into an ocean on Mongo after being attacked during the final approach to the planet.
In the opening scenes, after being captured by Ming's Gill Men, Gordon, Arden, and Zarkov meet King Thun the Lion-man and Prince Barin of the forest-kingdom of Arboria. It is later revealed that an earlier king of all Mongo, more powerful than Ming, was named Gor-dan, and that he strongly resembled Flash.
 
Also included 
Flash Gordon (1980)
Defenders of the Earth : Escape Mongo (1986)