A good article written by an experienced breeder
The unique appearance of this so-called "dragon" betta is characterized by a thick, solid silvery/white metallic layer which almost resembles armor.
According to Pichet (Interfish breeder team - Thailand), the first "dragons" were created by using a "super" red plakat, a red copper plakat and Betta sp. mahachai . With some difficulty, the wild Betta sp. mahachai was crossed to the red copper plakat with the intent of preserving the Betta sp. mahachai traits in the offspring. Then a young male from this spawn was crossed to a super red plakat female. The third step was a mother x son backcross: the super red female was crossed to one of her offspring in a method commonly referred to as 'line breeding'. Although the body shape and finnage of the fry was not very good and some of them even showed malformations in the body, the color was there and the first dragon pair was born! The first "dragons" were developed by Mr. Tea. The "Red dragon V1" were first presented to the Thai public in the December 2004 edition of a magazine called "Fancy Fish" by the Interfish breeder team
Betta imbellis, Betta smaragdina and Betta sp. mahachai naturally have a higher degree of iridescence on the scales compared to Betta splendens which probably is an adaption to the murkier water in their natural habitat. Both "dragons" and "armadillos" described above are characterized by a thick metallic iridescent scaling which almost resembles body armor. When we have a look at the origin of metallics and "dragons" we see quite a lot of overlap. Outcrossing domesticated bettas to Betta imbellis gave rise to the metallics which in turn also have an important contribution to the development of the "dragon". This shared origin mostly likely explains the similarity between metallics and "dragons" but in case of the latter the additional influence of Betta sp. mahachai seems to be the key to the thick shiny armor-like metallic scaling. When we compare wildtype Betta imbellis and Betta sp. mahachai we can already see the iridescence is shinier and thicker in the latter.