The race known as the "Hostile Extraterrestrials", or "HETs" are a race of humanoid reptilian lifeforms, with very dark skin and a fairly large head, which houses their two brains; one main one at the back and a smaller one at the front which repairs the larger if it is damaged.
They invaded the planet Earth in the year 2032, sparking the first conflict between Humanity and being from another planet. This invasion became known as the War of 2032.
The HET who fought against humanity in 2032 were observed to be split into seven different castes. These include:
The Infantry Caste, which are far more muscular than a human, and have powerful weapons protruding from their arms instead of grasping hands. Their average height is about 9' 5".
The Warrior Caste (pictured), which are similar to the above caste but do not have firearms connected to their arms, and instead have grasping hands, with three digits on each hand. Their average height is 9' 3".
The Commander Caste, which lead squadrons of infantry and warrior HETs into battle. These are differentiated from other castes mainly by their taller yet wider bodies. Their arms have grasping fingers similar to warriors but their fingers can retract into their arm for it to become a blaster cannon. Unlike other castes, the heart of the commander is where a human's stomach would be. This is to make room for their largest weapon, their chest cannon. Their chest appears to have an empty hole in the middle, but in actuality, it is where their chest cannon comes from. Light energy from around the rim of the hole join together in the centre and fires at the direction the individual chooses. Their average height is 10' 3"
The Scout Caste, who conduct reconnaissance missions in teams of 3-5 individuals to gather information about the enemy's positions, strength, and movements. They do not possess much weaponry, being equipped with a simple blaster rifle. They're the shortest of the castes with an average height of 6' 5", which helps them go more unnoticed than their brethren.
The Pilot Caste, which have biological connections with the aircraft they fly. If the vehicle is damaged, the pilot feels it. They connect to the craft via placing their hand into the aircraft's "brain" which link the two together. They do not have any other weapons as their only job is to fly the ships. Their average height is about 7' 7".
The Cavalry Caste, which ride on biomechanical quadruped creatures known by humans as BMASs (pronounced "Bee-Mass"; Biomechanical Alien Steeds). A HET rider is connected to their BMAS biologically from a young age. They grow up together, train together, die together. They are distinguishable by their broad legs and long arms.
The Intelligence Caste, who specialize in their namesake, gathering information and laying down lines of communication. Unlike other HET castes, the Intelligence Caste lacks any integrated weapons systems. The lack of weaponry is made up for by their ability to utilize both grasping hands, which they use to operate machinery and vehicles, such as driving ground artillery platforms and operating walking guns. Their average height is about 7' 1".
They do not have a single homeworld, but actually have two, which are both similar in size, atmosphere, and temperature to Earth and they both orbit each other around a centre point. The two planet's civilizations were separated for thousands of years until one of them developed space travel and ventured to the other world. After this, the two peoples shared their resources and managed to vastly improve their technology and eventually invent the wormhole, allowing them to transport themselves to new worlds and invade it.
The HET have colonized several 1000 worlds across the Milky Way galaxy, commonly fighting their inhabitants into extinction. They do this as part of their religion, which instructs them to spread their civilizations so that a global apocalypse would not bring about the end of their species. This was a result of a similar apocalyptic event that occurred on one of their homeworlds 500,000 years ago.
Due to it being an older and more populous civilization with more resources than Humanity, the HET have much more advanced technology. This includes:
The most advanced piece of technology in the possession of the HET is the wormhole, a shortcut connecting two separate points in space. This allowed them to transport vast amounts of their military to other planets in order to conquer it, as well as provide commercial transportation between worlds already under HET control.