King Astro Nightus is an alicorn, the previous ruler of Equestria, the father of Princess Celestia and Princess Luna, and husband of Queen Heavenslight. His history is unknown, but is known that he was the Keeper of the Moon and the stars, also controlling comet rotations and sometimes meteors. But he was killed by Captain Taiklar Blackheart, and robbed of his soul. But Celestia managed to defeat Taiklar, and bring back her parents. Nightus decreed to resume his duties as the controller of the stars and space and leave controlling the Moon to Luna. Now, he is rarely seen in Equestria. The only times he comes is during an eclipse with his wife, and during meteor showers and comet appearences.
Nightus was born as one of the second last Alicorn Gods in Equestrian history during the times leading up to the deadly Chaos War of the First Cartoonian War. He had made friends with Heavenslight and formed more of a special connection to each other. Their parents were sure that they would both take their places as controllers of the sun and moon just like their ancestors and the rest of their kind were destined to control the aspects of Equestria's nature. But when the Chaos War started, Nightus and Heavenslight's parents told them to stay hidden in the shadows until they would return from fighting in the War. But as the years passed, the two never heard from their parents again. When the Chaos War ended, they went out of hiding and discovered that the Sun that Heavenslight was destined to control was unstable and was being controlled by mortal unicorns. In fact, most of the aspects of nature were being controlled by the mortal ponies. The two embarked on a quest to search for their parents, not knowing that they had perished when using the Elements of Peace to defeat Tyranny. They continued this adventure for 8 years discovering lost Alicorn artifacts and clues on their parents' deaths. Then they discovered a group of unicorns that were struggling to control the Sun and most were collapsing of exhaustion since they couldn't do perfect work like their Alicorn Gods did. Showing concern for these poor souls, Heavenslight was able to show up and raise the Sun perfectly and gained her cutie mark. The ponies were surprised to see a surviving Alicorn God, and Nightus and Heavenslight, since they had discovered that they were the last Alicorns left in Equestria, dedicated their lives in protecting Equestria and maintaining the peace their ancestors had taught them to maintain. Nightus would eventually discover how to control the Moon at the same affect, and gain his cutie mark. They weren't very happy to discover that their parents were killed during the end of the Chaos War, but they discovered that the Draconequui, the creatures that waged the war, were reformed of their evil ways and Nightus and Heavenslight were able to end their discrimination problems. They even discovered that they loved each other, got married, and gave birth to Celestia and Luna.
The rulers of the Draconequui, King Wacky and Queen Pranks, at the same time gave birth to their second son, Discord, after their first son, Mayhem, was corrupted and banished. Celestia, Luna, and Discord grew up as acquaintances, but Discord never found the sisters true friends. The three had played together in a location in the Draconequus homeland called Eris Caves, where they drew paintings on the walls, and had a side-view of the sea and the beautiful sky. Wacky and Pranks, fearing that Discord would end up like Mayhem, told him about the Chaos War and asked him to be careful with what path he chooses to follow. But when Celestia, Luna, and Discord reached maturity, Discord was captured by Mayhem, and he was tricked into joining his side, and the two overthrew Nightus and Heavenslight, and turned them and their daughters into monstrous creatures called Serpicorns. Discord became the prime ruler of Equestria, and Mayhem became the leader of his elemental guards. The Celestial family was able to convert themselves back into their Alicorn selves after convincing their daughters, which had lost hope after being enslaved like all other Serpicorn creations, into seeing that their pony subjects were worth fighting for. So with help from Star Swirl the Bearded, the Celestial Sisters were told to find the Tree of Harmony and use the Elements of Harmony which they possessed to defeat Discord, and turn him to stone. Mayhem unfortunately escaped since he was much more powerful, and Nightus and Heavenslight cast a protective shield around Equestria to ensure that Mayhem doesn't get revenge, and Discord remains petrified.
However, as years started to pass, and after defeating a fearful villain named Pitch Black who caused the Great Equestrian Fear War, Nightus and Heavenslight were lost to Celestia and Luna after an other-worldly Keyblade-wielding pirate named Captain Taiklar Blackheart arrived and absorbed Nightus and Heavenslight's souls, killing them and leaving Celestia and Luna in charge of Equestria ever since, and causing the events that would lead to Luna becoming Nightmare Moon. Celestia wasn't very happy of losing most of her family now that she was the only one left to rule Equestria. Eventually when Luna is cured of corruption, the two would fight to get their parents back.