Astra Dark is an evil version of Astra that appeared in the Ultraman Legend stage show in 2014. There is almost no difference in appearance from the real Astra besides the glowing red eyes.
History
Astra Dark and his brother, Leo Dark, were summoned by the power of the Dark Spark by Alien Nackle Gray. He had the same abilities as the real Astra and was able to put up a real challenge for Ultraman Zero.