The generalised classification Humanoids is defined by the Encyclopaedia Cosmosica as "any species with at least one head, four limbs, an upper and lower trunk, and an upright, bipedal, bilaterally symmetrical body stance." Two of the most prominent examples are the dominant life form on the planet Kayaclasch and the Earth mammalian order Primates. Others include Barbartronians, Sectotans, Slythins, and Temans.

With regard to the prevalence of the humanoids throughout the universe, convergent evolution provides the most likely explanation of how otherwise unrelated species may evolve almost identical traits, including bipedalism and other humanoid skeletal features, as a result of similar evolutionary pressures. A more controversial hypothesis is so-called "morphic resonance", in which biological phenomena theoretically increase in probability after initial occurrence and therefore evolutionary patterns are established by prior similar forms. There is a rumour, however, that the founder of the Infinity Knights would visit assorted species across the galaxies during their important evolutionary stages in order to influence their development towards the humanoid form.

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