In 2369, the Miradorn twins Ah-Kel and Ro-Kel raided a Vanoben transport with their Miradorn raider just two light years from Deep Space 9. Shortly thereafter, they appeared at Quark's attempting to sell the Ferengi the stolen item; a valuable, ornate egg metal sphere. In a botched robbery attempt masterminded by Quark, a Rakhari fugitive named Croden killed Ro-Kel. In retaliation, Ah-Kel vowed to avenge his brother's death, his only purpose left in life, but died trying. (DS9: "Vortex")
In 2373, prior to the outbreak of the Dominion War, the Miradorn signed a nonaggression pact with the Dominion. Odo considered this to be an impressive inroad into the Alpha Quadrant for the Dominion. (DS9: "Call to Arms")
Miradorn were large humanoids with pale skin. They had distinctive foreheads divided into two hemispheres (which seem to have been bones), and also distinctive structures on the throat.
Miradorn culture included the belief that a pair of twins together formed two halves of one being, resulting in twinned Miradorn having an extremely close relationship. If one twin died, the other twin would anguish in the loss of "self".
According to the script, the Miradorn were described as "hulking aliens".
The Miradorn makeup was one of makeup supervisor Michael Westmore's favorite designs from the first season of Deep Space Nine. In particular, Westmore liked the throat area. Originally, the throat had been designed with a loose flap of skin hanging down over the Adam's apple. However, costume designer Robert Blackman wanted to use a necklace as part of the Miradorn costume, but Westmore felt that to place a necklace over the flap of skin would render it useless and spoil the effect. As such, it was decided to run the necklace under the flap of skin, and glue the skin down at the bottom, so it was no longer loose. Westmore has stated that he would like to explore this type of design again in the future. (Michael Westmore's Aliens: Season One, DS9 Season 1 DVD, special feature)
Miradorn shared a strong likeness with the previously-seen Ktarians, both having double-lobed foreheads and similar brow features, but lacking the aforementioned skin flap on the throat. For more information these similarities, see the full analysis at Ex Astris Scientia.
According to the ebook The Cleanup, the Miradorn homeworld was called Mirada. 90% of the Miradorn population consists of telepathically-linked twins.