Species

Throughout the Red vs. Blue series, several species have been introduced in the series. Currently, four sentient and intelligent species have been shown with some having sub-species.

Human
Humans (scientific name homo sapiens), also known as shisno by aliens in the series, are mammals relating to primates. Humans have a bipedal stance and a large brain in ratio with their bodies, allowing them to become the most advance and intelligent lifeforms originating from their planet. In the series, many humans are seen to wear armor to protect their bodies. Naturally from Earth, when humans mastered interstellar travel, they began to colonize other planets due to their growing population. However, they soon discovered hostile alien life. This led to the Great War, which went for many years and ended before the events in the Recollections. Most of the characters in the series are human.

Cyborg
Considered a "sub-species" of humans, cyborgs (short for cybernetic organisms) are humans who both have organic and artificial body parts. Cyborgs' artificial parts serve as technological enhancements that provide aid for the host, such as a robotic limb to aid in movement. Due to these cybernetics, cyborgs can be sometimes stronger or smarter than humans, but they have the disadvantage to maintain these artificial enhancements. Currently, only two cyborgs have appeared in the series: Simmons and the Demo Man.

Artificial Intelligence
Artificial Intelligence, commonly abbreviated A.I., is an artificially created construct that exhibits intelligence similar to a sentient being. Most A.I. physical appearances have a body that relate to their designed purpose. A.I. have the possibility to go rampant, a process of going insane, after a specific amount of time. However, if they survive the four stages of rampancy, the A.I. can, theoretically, be considered a human being. Dozens of A.I. appear in the series, with some playing a major role in Red vs. Blue. There are two main "sub-species" of A.I.

Ghost A.I.
Ghost A.I. are A.I. that lack a physical body who are programs that use holographic constructs to give themselves a unique appearance (otherwise known as an avatar). Due to the lack of a physical body, they have been called ghosts on occasions. Some of these A.I. have the ability to "jump" into objects and armor to aid themselves or their host, such as by running armor enhancements and functioning a vehicle. On rare occasions, these A.I. also have the ability to take complete control of their hosts and vehicles. Notable "ghost" A.I. include Church, Tex, Epsilon, and Omega.

Robot
Another "sub-species" of A.I., robots are machines that performs various complex acts for its creator. Although having a physical body, robots tend to be less advance than "ghost" A.I., as they usually tend to lack free will and only follows its programming. Notable robots include Lopez, Freckles, and Lopez 2.0

Alien
Aliens are creatures that aren't of Earth origin; simply species originating from another planet that isn't Earth. They have also mastered interstellar travel before discovering humans. Due to hostile actions, the Great War began between the Covenant (a group of alien species) and humans before ending years later after the events of the Blood Gulch Chronicles. In the series, aliens don't have a major role and few appearances, which gives little info about certain species.

Sangheili
Sangheilis, more commonly called elites by humans, are a species of aliens that have a bipedal stance, 2 fingers and thumb, dark skin, and mandibles. Elites are the most common aliens seen and, after the Great War, became allies to the human species. In the series, elites are only known to communicate in two ways: through blargs and honks or using different pitches of sound to speak. They are also shown to be very religious about ancient technology and their prophecies, such as the Great Quest. Some of the only known elites include the Blue Alien, Junior, and Smith.

Huragok
Huragoks, more commonly known as engineers by humans, are a race of biological supercomputers. Their exact appearance is unknown in the series as only there shadow is shown, but they seem to have the ability to float in mid-air and have several tentacles. The only known huragok in the series is the Engineer used by Project Freelancer to create the fragmented A.I.

Non-Canon
In some non-canon material, other species have been shown in the series. For example: in Red vs. Blue: Animated, several species aligned to the Covenant are seen during the rescue attempt to save Sarge and Tex. This includes grunts, jackals, and brutes.

Trivia

 * The reason why elites are the most common alien species seen in the series is that they're (most commonly) the only other species to play as in the Halo franchise.