Last week on Supergirl, Kara (Melissa Benoist) got a shock when she discovered a cult in National City, devoted to worshiping... her. She found a leaflet on the organization, and went to meeting to discover that this new religion was led by a passenger on the very first plane that she saved. He brought together others that had also been saved by Supergirl, people who shared their stories and believed that they were special by virtue of having been saved.
To up the strangeness factor, the cult called themselves the Children Of Rao, and their meetings and services were loosely based on the religion of Krypton. Not only did this appall Supergirl, who was upset at how Rao's teachings were being twisted, but it also confused her; how did these people know so much about the Kryptonian faith? Throughout the episode, Kara learned that the leader of the Children of Rao had found a probe sent out by the Kryptonians, including an obelisk with some of the teachings of Rao.
The cult itself is concerning for Kara (and because cults are always a little concerning in general), especially when she learns that people are intentionally putting themselves in danger in order to be saved by her. Finally, they even try to use the probe to blow up a packed stadium, as a baptism for all the people inside. Supergirl saves the day (obviously), but Kryptonite in the probe prevents her from doing it effortlessly, and many of the faithful run away from her once they see her in a weakened state. It's a vaguely creepy look at how people might react to a superhero in their midst, and it's not the first time that the Super-family have been worshiped.
Who Is Rao, The Kryptonian God?
Rao himself is the ultimate god of the Kryptonians, and the worship of Rao seems to be the only faith on Krypton. Rao is a the deity who created the universe, including other, lesser Gods and the planet Krypton itself. He is associated with light and the sun, and is seen as a benevolent presence. The church of Rao is led by hooded priests, the most senior of which is known as the Voice of Rao, and the history of these priests goes even farther back than the history of the House of El itself. 'Superman: Blood Of My Ancestors' revealed the earliest history of Kal-El's house, when El himself was resurrected by Rao in his temple, and given the power to re-build Krypton.
The idea of the Kryptonian faith being housed in a probe is also seen in the comics, although the details of the story differ from what was seen on 'The Faithful'. In the Post-Crisis history of Krypton, an alien ship landed on the planet, a sentient 'preservation ship' designed to save the culture of the aliens. However, a Kryptonian killed the aliens and took over the ship, altering it to preserve Krypton's culture instead. Once sent to a new world, the ship (called the Eradicator) would destroy the existing culture, and replace it with a New Krypton. It's a concept that is a little more violent than the Supergirl idea of a purely educational probe, but at its core, the Eradictor of the comics and the probe of Supergirl do the same thing; introduce Kryptonian faith and culture to Earth.
Super-Cults In Comic Books
The worship of Rao, however, is not the primary focus of the Children of Rao in Supergirl. Instead, the group is dedicated to the worship of Supergirl herself; and it's not the first time that a group of humans has decided to worship a Kryptonian hero, either. There have been several storylines in the DC universe that involve people following Superman as a God, although these groups are generally small or short-lived.
Superman himself has been worshiped more than once. In 'Batman/Superman: Worship', Superman is away on another planet when Batman discovers a cult of Superman worshippers plotting to murder Lois Lane. Unaware that Clark Kent and Superman are the same person, they believe that Lois's marriage to Clark is an insult to Superman, and intend to literally burn her at the stake for her 'crime'. Obviously, Supes himself isn't particularly happy with a bunch of wife-murdering, human-sacrificing worshipers, though, and the cult comes to an end. In 'The Kingdom', Superman is worshiped once more, by William Matthews. A human who survived a nuclear disaster, William became obsessed with Superman, launching the Church of Superman and worshiping him as a God. However, William was later driven insane and became Gog when he gained powers, and lost faith in Superman. His obsession flipped, and instead of worshiping him, he hated him, and sought to destroy him and any other 'gods' he could find. Various lesser 'worshipers' and believers have also popped up in a few storylines, as a response to Superman's heroics.
Superboy has also had a cult devoted to him, the Cult of Connor. After his death, a group rose up to worship Superboy, believing that one day he would return. As resurrectionists, they believed not only that Connor could be brought back, but that others could be as well. This cult fought against death, and used Superboy as a figurehead to focus their obsession. They also worshiped Rao, set up altars with Kryptonian crystals, and inverted the 'S' symbol to take as their own. The cult only ended when they discovered that the resurrection rites could only happen once, and their hopes of bringing back their loved ones were dashed.