Wikipedia
Kryptonians are a fictional extraterrestrial race of humanoids within the DC Comics universe that originated on the planet Krypton. The term originated from the stories of DC Comics superhero, Superman. The stories also use "Kryptonian" as an adjective to refer to anything created by or associated with the planet itself or the cultures that existed on it.
Members of the dominant species of the planet Krypton are indistinguishable from humans in terms of their appearance; their physiology and genetics, however, are vastly different-in some continuities Kryptonians are difficult to clone because their DNA is so complex that human science is not advanced enough to decipher it. The cellular structure of Kryptonians allows for solar energy to be absorbed at extremely high levels. On the planet Krypton, whose parent star has often been depicted as an ancient red supergiant with a relatively low energy output, their natural abilities were the same as humans. When exposed to a young yellow star like Earth's Sun, which is much smaller than their own sun and with a vastly higher energy output, their bodies are able to absorb and process so much energy that it eventually manifests as vast superhuman powers (such as superhuman strength, superhuman speed, invulnerability, flight, x-ray vision, heat vision, and superhuman senses).
Almost all Kryptonians were killed when the planet exploded shortly after the infant Kal-El was sent to Earth. In some continuities, he is the planet's only survivor.