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Kryptonians are a species of humanoid aliens from the planet Krypton. On the surface, they are visually indistinguishable from Humans from Earth; however, they have evolved many complex physical differences. Superman, Supergirl, Krypto and General Zod are all examples of Kryptonians living on Earth.
First introduced in Action Comics #1 (1938) by creators Jerry Siegel and Joe Shuster, Kryptonians have undergone several retcons across decades of continuity, but core elements of their physiology remain consistent in modern depictions.
Evolutionary History
Kryptonians evolved on a world of extreme conditions: immense gravity (often depicted as far stronger than Earth's), geological instability from an unstable uranium core, and radiation from a red sun. These pressures favored dense, resilient cellular structures and highly efficient energy metabolism. Early life on Krypton faced deadly flora and fauna, driving rapid adaptation toward physical durability and intellectual advancement.
In the Golden Age (1938–1950s), Kryptonians were portrayed as naturally superhuman even on their home planet. They possessed peak physical perfection able to leap great distances, run at high speeds, and withstand heavy impacts due to Krypton's massive size and gravity. Earth's lower gravity amplified these traits, explaining Superman's early powers of super strength, speed, and leaping (not yet flight). Influences included John Carter of Mars stories, where lower gravity granted enhanced abilities. Siegel and Shuster described Krypton as a huge planet, making its inhabitants inherently stronger, with powers heightened on smaller worlds.
By the Silver Age and later continuities, the origin shifted: Kryptonians under Rao's red sun were physiologically similar to peak humans—strong, long-lived, and intelligent—but without overt superpowers. Their cells evolved to efficiently store and process stellar radiation as a survival mechanism in Krypton's harsh environment. This adaptation remained dormant under red sunlight but activated explosively under yellow solar radiation, which provides higher-energy photons. The photonucleic effect (or solar energy absorption) became the primary explanation: Kryptonian cells absorb, store, and metabolize yellow sun energy, fueling extraordinary abilities.
Krypton's destruction left the species nearly extinct, though survivors (including bottled cities like Kandor) and colonies have appeared in stories, such as the New Krypton arc where 100,000 Kryptonians briefly formed a society on Earth or nearby.
Physiology
Kryptonians share a strikingly human-like appearance: bipedal with two arms, familiar facial features, skin tones varying across ethnic groups (from light to dark, reflecting convergent evolution similar to Earth's diverse populations), and average heights typically around 6 feet (though taller or shorter individuals existed). This external similarity allowed seamless integration with humans on Earth once depowered. Internally, however, their biology diverges dramatically even without superhuman enhancements. Their cellular structure is denser, more resilient, and biologically superior, often described as the "greatest organic power storage units in the known galaxy." Cells form a sophisticated bio-cellular matrix tied to the body's electromagnetic field, enabling hyper-efficient energy use and storage far beyond human capabilities. On Krypton—under the red sun Rao and the planet's significantly higher gravity—these advanced traits manifested subtly but meaningfully. Without the high-energy yellow solar radiation to trigger full activation, Kryptonians operated at roughly peak-human or slightly enhanced human levels in terms of raw physical strength and speed. They lacked flight, heat vision, X-ray vision, invulnerability to extreme forces, or any of the overt superpowers associated with Superman. However, their physiology still provided clear advantages shaped by evolution on a harsh world.
Powers and abilities
See: Kryptonian Powers
Kryptonian costumes
List of Kryptonians
- Superman / Kal-El / Clark Kent
- Jor-El
- Lara
- General Zod
- Seyg-El
- Cir-El
- Ter-El
- Don-El
- Faora (a.k.a. Ursa, Mala, Zaora, and more in various media).
- Doomsday (Davis Bloome)
- Jason White (half Kryptonian/half human)
- Raya
- Supergirl (Kara Zor-El/Linda Lee)
- Superboy / Kon-El / Connor Kent (human-Kryptonian clone hybrid.)
- Power Girl (Kara Zor-L/Karen Starr)
- Superman Legacy
- Val-Zod
- Jonathan Samuel Kent / Superboy (half Kryptonian/half Human)
- Krypto (Dog)