Kryptonians are humanoids externally very reminiscent of Earth’s humans, but their internal biology is much different. Their cellular function allows them to absorb solar energy at extremely high levels when exposed to a yellow star like Earth's Sun, giving them vast superhuman powers such as flight, super strength and speed, invulnerability, heat beams emission and heightened senses (super hearing, x-ray vision, telescopic vision, micro-vision), super breath, and freezing breath. When superpowered, they are subject to an allergic reaction to Kryptonite, a common mineral from their homeworld..
Kryptonians were a highly technologically advanced but non-expansionnist and intensively xenophobic civilisation. They developed cloning and genetic engineering and a unique technology based on self-grown crystals which made up the vast majority of their planet's surface. Vast amounts of data and information could be stored on relatively small crystals for all the knowledge obtained by the Kryptonians throughout their history. Each Kryptonian family was called a "House," and was represented by a crest or symbol, often worn by the head of the house.
Their homeworld Krypton was an earth size planet orbiting the red sun Rao some 50 light-years from our solar system.
Over 100,000 years ago, Kryptonians had already conquered disease, learned to retard the aging process, and perfected cloning; vast banks of non-sentient clones held multiple copies of each living Kryptonian so that replacement parts were always available in the case of injury. All Kryptonians were effectively immortal and eternally young, and enjoyed an idyllic, sensual existence in an Arcadian paradise.
Then came the debate as to whether clones should have rights. Eventually this disagreement ignited the Clone Wars, during which Kryptonian science was turned to warfare and several super-weapons were developed and used.
Krypton was left deeply scarred. The formerly lush garden world was burnt and blasted, left mostly a lifeless desert. A sterile, emotionally dead civilization emerged from the ashes. Individuals became isolated from one another, living in widely separated technological citadels and shunning all personal, physical contact. Procreation became a matter of compatible genetic material selection which would be placed within an artificial womb called a "birthing matrix." Any attempt to contact other worlds was forbidden, and the planetary government maintained an isolationist stance, forbidding space exploration of any kind.
Then came the mysterious "Green Plague", killing Kryptonians by the hundreds. It is in that period that it was discovered that as a side effect of the war’s super weapons, growing radiation was produced by Krypton's increasingly unstable core. The planet exploded shortly after. Only one child survived, sent to Earth in its birthing matrix by its parents.
Before the Clone Wars, some Kryptonians had left their homeworld and established themselves on Daxxam, a planet orbiting the red giant Valor, so while on their homeworld, they do not have superpowers. They are fatally sensitive to lead, which affects them as kryptonite affects Kryptonians. They are an intensely xenophobic race, and are fearful of alien invaders. Although Daxamites tend to stay on their homeworld, some have ventured into the galaxy. Valor’s location is not known but is presumably in Rao’s vicinity.
The Daxamites learnt about humanity when they took part in an invasion of Earth masterminded by the Dominators in 1988-89. During the invasion they discovered that they gained tremendous powers, of a set and scale comparable to Kryptonians, in a yellow sun environment. However, when they were helped by the locals while succumbing to lead poisoning, they withdrew from the Alliance.
They are most probably the same species known as the Dakkamites from the planet Dakkam, in the Beta Rigel star system in the Milky Way galaxy. grants them super- Known Dakkamites include Wundarr the Aquarian and Quantum.