The Zentradi are a race of genetically engineered giants. First created over a hundred thousand years ago by the Protoculture for the sake of carrying out proxy warfare, they range from around 9 meters tall (most Meltrans) to nearly 14 meters (Commanders). Almost genetically identical to humans, Zentradi are also the males of the species. Female Zentrans are actually called Meltrans. Originally the two never occupied the same space. Both male and female warriors were created and kept separate so as to foster different fighting styles.
As they were bred to be warriors, Zentradi have a very potent fighting instinct that makes them generally predisposed towards violence. Originally Zentradi did not reproduce sexually; in fact, the very idea/display of males and females together in an intimate manner tends to give rise to extreme fear and confusion in regular Zentrans. Until recently all Zentradi came exclusively from cloning matrixes. Nearly all original Zentradi are warriors, bred for combat and largely unable to even repair their own equipment which forces them to rely on automated repair systems. The only known exception to this are Zentradi advisors, specially bred Zentrans and Meltrans who sacrifice raw physical power in favor of vastly expanded intelligence. Advisors are effectively walking archives, carrying a large amount of information with them, including ancient Zentradi lore.
Along with seeing men and women together, Zentradi are also susceptible to another form of culture shock: music. Zentradi with no prior contact with such things will again find themselves thrown into a state of confusion (and occasionally fanboy/fangirl squealing) when they are exposed to music. In the aftermath of Space War I, almost all known Zentradi have integrated into human society (much thanks to the marriage of Millia and Max Jenius). As Zentradi are able to reduce themselves to human size (through a process known as Miclonization) they have become very much like their human counterparts. The only things that visibly set Zentradi apart from humans at this level is their skin and hair pigmentation can be quite different as well as possessing pointed ears and slightly more pronounced canines. Even stranger is some Zentradi can develop hair that moves almost akin to antennae, making them extremely emotive at times. It isn't unheard of for a Zentradi to have blue tinted skin or neon pink hair, however there are some with very normal skin and hair tones as well. The other things that separate Zentradi from humans is they still possess their fighting instinct and increased physical prowess (most advisor Zentradi meanwhile seem to prefer to remain full sized to preserve their disproportionately enlarged brains). Miclone Zentradi are also capable to reverse the process and return to their original size. This process can be completed within a few minutes with the proper equipment, though it should be noted sometimes genetic defects can cause some odd side effects - such as the Zentradi's body being at differing levels of maturity depending on whether in their Micron (human) or Macron (giant) forms.
Zentradi are also fully capable of reproducing with humans due to their nearly identical genes and despite the vastly different phenotypes that develop as a result.