Worship of Rao and Gods associated with him is the only religion known to have existed on Krypton. Rao is hailed as the creator deity of Krypton and the Kryptonian people.
According to the Kryptonian mythology, Rao is the first being to be born out of the void before the universe. Feeling lonely, he sought to bring order to the chaos from which he was born, and thus created the universe. After countless eons of ordering the cosmos, Rao created Krypton, a planet meant to be a jewel in his creation.
Rao then created all the other Kryptonian gods from his own essence, and these godlings called him "Father Rao". Among Rao's children were Nightwing and Flamebird and Vohc the builder. Vohc would later become the first heretic, a satanic figure in the Kryptonian mythology.
It is also known that, long before the rise of the Kryptonian civilization, Rao waged a war with Cythonna, Goddess of ice. This
was known as "the Wars of Fire and Ice." Rao defeated and imprisoned the evil Goddess, though she would later escape and seek revenge on Kal-El, the last child of Rao.
It is also hinted in Endless Nights that Rao is, in fact, responsible for Krypton's destruction, and Kal-El's survival as the last son of Krypton. This is seen when Despair, one of the Endless has a conversation with him, and tried to convince him how beautiful it would be for life to rise in such an extreme environment, only to have it die out and a single child left to mourn it. It is unknown if Rao shared the opinion. However, whether or not this was the god Rao or if it was a living embodiment of the star Rao (or if there even is a difference between the two) is unknown.
Priests of Rao
On New Krypton, Rao, and all the other Gods are worshiped by the Religious Guild. While every Guild has a patron God, Rao is considered the God of the entire Kryptonian civilization, and is thus honored by all the Kryptonians.
Rao's high priest is known as the voice of Rao. He wears a bright red mask which conceals his face. He is present on the assemblies of the High council, and apparently holds considerable power with them, at least when it comes to judicial decisions, as he was able to give Kal-El a pardon on the eve of a Kryptonian holiday. He is believed to channel the actual voice of Rao, and as such he rarely speaks, and when he does, it is only in matters of utmost importance. After all, a God does not engage in pointless chitchat.
Reincarnation of Rao
Recently, Jax-Ur, an avatar of Vohc, used a sample of Thara Ak-Var's, avatar or Flamebird, DNA to create a massive artificial creature which he claims is the reincarnation of Rao. This behemoth resembles Rao dotted with Kryptonian sunstone crystals. The creature seems unstoppable, as it simply absorbs any energy sent against him and uses it to grow.