Astra is the younger twin brother of Ultraman Leo and a prince of the fallen Planet L77. He came to Earth after learning that Leo had survived the destruction of their home planet and has appeared several times to assist his brother.

The younger brother of Ultraman Leo, Astra formerly lived on L77, a planet in the vicinity of the Land of Light whose inhabitants became Ultras after the effects of the Plasma Spark being activated in Nebula M78 reached L77. After the destruction of L77 by the Alien Magma, Leo, Astra, and Leo's pet monster Ron were the last survivors, although at the time Leo was unaware that the other two had survived. While Leo and Ron separately made their way to Earth, Astra was captured and held prisoner by the Alien Magma until he was eventually rescued by Ultraman King. After King told him of Leo's survival, Astra headed for Earth and rescued his brother during a battle against Garon and Littre. Ever since, Astra has assisted Leo in fighting several different aliens that were too powerful for Leo to defeat by himself.