The Space Triptych first crystallized in the original Alien vs. Predator comics. Dark Horse Comics was looking to create a crossover series using properties to which they had access. Alien vs. Predator was understood immediately to be a strong concept because of the popularity of the Alien and Predator franchises and because the differences and tensions between Humans, Predators, and Xenomorphs create the opportunity for very interesting conflicts. Other Sci-fi designers for games, likely inspired by these tensions, created similar patterns in their universe designs. Eventually, this pattern became recognizable as an archetype.
The Space Triptych archetype involves three conflicting races. These are humans, advanced aliens, and monster aliens. Each type of race carries with it a few characteristics that further define the archetypal tensions. Commonly, Monster aliens embody an existential threat against the other races, forcing them to ally with each other. These alliances are often limited to individual heroes.
In a Space Triptych situation, Humans are the most instantly recognizable and relatable characters, and are near-universally depicted as "the good guys". The baseline for this representation of Humans appears to be inherited from the Alien films and their associated games. These Humans are typically spacefaring, but their technology tends to be recognizable as extrapolations from contemporary machinery. Weapons are generally advanced versions of today's paradigms, including projectile-based assault rifles, machine guns, and artillery. Vehicles often carry a utilitarian, military design. The most apparent political power structures (at least those depicted in the conflict) tend to be military or corporate, each of which motivates characters with some standard biases and prejudices.
Examples of these types of Humans include Terrans, Colonial Marines, and the UNSC.
Advanced Alien races are portrayed as having lived with much higher technology for a much longer time, and are usually much older species than Humanity. Their technology tends to be energy-based, arming them with things like plasma rifles, cloaking devices, and teleportation. Their vehicles tend to be manoeuvrable and sleek, yet extremely powerful, and most tend to hover or fly. Many of these aliens are also physically superior to Humans, having large stature, incredible strength, and sometimes psionic abilities. These races tend to create rigid political environments and strict orthodoxy, including fanatical devotion to religious and/or tribal affiliations. Further archetypes include races placing great value on personal ability, particularly martial strength, and many live by strict codes that demand loyalty, obedience, and a set of warrior's ethics. Advanced Aliens tend to be extremely defensive, if not openly hostile to other races, although they sometimes form shaky alliances with Humans when combating a Monster Alien threat.
Prominent forms of these aliens include Predators, the Protoss, and the various races that make up the Covenant, especially the Elites.
In contrast to Advanced Aliens, "Monster" Aliens often employ little to no technology. Some are still spacefaring, but they tend to use a combination of biological means and appropriated external technology. Monster Aliens rely on an insidious (often parasitic) reproductive cycle and their extremely dangerous physiology to battle more technologically-oriented races. Many have hardened carapaces and sharp teeth and claws, while some can do things like spit acid or infect and assimilate their enemies. While the Advanced Aliens are further along the technological development chain than Humans, Monster Aliens tend to be much farther along the evolutionary development chain than either; Monster Aliens are generally so physically powerful that their bodies alone allow them to take on Human and/or Advanced Alien military units, at least in large numbers. Populations tend to be massive, to make up for the relative weakness of the individual. Monster Alien races are often controlled by a singular intelligence, which can take the form of a brood queen or hive mind. Subservient creatures tend to show no individuality, and will act together with unified purpose. Some master intelligences are capable of communicating with other races, usually to transmit a message of arrogance and doom, while others are not. Most who can communicate are telepathic.
Archetypal monster alien races include Xenomorphs, the Zerg swarm, and the Flood.
Although these three templates are the most commonly used in science fiction settings, they are by no means absolute; the Supreme Commander games depict three different factions of futuristic Humans, though the vast differences in their technology echo some of the concepts in the triptych, with the United Earth Federation being similar to the archetypal "Human" race in the conflict, and the Aeon Illuminate's sleek ships and energy weapons being similar to the "Advanced Aliens" race. Furthermore, some games include deliberate changes to these roles; in the 2015 strategy game Grey Goo, the "Advanced Aliens" are the Human race, who have developed technologically to the point where their 'military' consists of remotely-piloted hoverdrones armed with energy weapons, while the alien Beta species, which has an industrial look to their technology and utilizes gunpowder-based firearms and explosive weapons, fits into the "Human" slot as the most familiar extrapolations of modern technology. Additionally, while it is not as big a change as the other two, Grey Goo's "Monster Aliens", the Goo, stand out somewhat for being entirely technological, as the Goo are clusters of nanomachines that seek to consume all matter in the universe for the purposes of self-replication.