In the universe of the Star Trek television programs and films, the Andorians are a race of blue-skinned, white-haired, antennaed humanoids who were one of the founding members of the United Federation of Planets.
Physiology
The Andorians hail from the icy moon Andoria, which orbits the ringed gas giant Andor. Other than their white hair, Andorians are pretty much entirely blue, with blue eyes, blue blood, blue teeth, blue lips, and blue gums. In order to survive in their freezing cold native environment, they have a very high metabolism compared to humans and require a very high intake of food. But despite the coldness of their world of origin, Andorians are very hardy and can actually survive in almost any temperature, up to and including the boiling point of water on Earth.
The Andorians have a pair of antennae sprouting from their temples which are fully prehensile and can move independently of each other. The main function of antennae for balance, and if one or both are cut off, the Andorian will be severely incapacitated for several months until they grow back (much like a lizard's tail). Another function of the antennae is to show emotion through various positionings. For example, sagging antennae show sadness, perky antennae show excitement, and Andorian antennae tend to point in the direction of another Andorian they are attracted to.
Andorians have four different sexes - shen, zhen, chan, and thaan - with the shens and zhens appearing more female to human eyes, while the chans and thaans conform more to human ideas of maleness. The female types are taller and more sexually aggressive than the male types. One member of all four sexes is required for a proper Andorian marriage, although only one of the female types and one of the male types is needed for reproduction.
There is also a subspecies of Andorians called the Aenar who live under the polar ice cap in Andoria's frozen northern wastes. Presumably due to living underground for millenia, the Aenar have grayish-white skin and are blind, but have enlarged, telepathic brains which they can use to "see". The Aenar are a subspecies and can interbreed with regular Andorians, producing highly intelligent, pale green-skinned offspring.
Society and Culture
Andorians are frequently described as a deeply emotional, passionate, and even violent race. They are extremely talented at art, and the Andorian Art Academy is said to be the best in the entire Federation. Andorians are extremely vulnerable to phased energy weapons, which give them a deadly infection, which may be the reasons why Andorian energy weapons have no stun setting, and why even in a time of energy weapons, Andorian officers still carry blade weapons with them at all times. Of particular importance is the ushaan-tor, a blade used by traditional Andorian iceminers, which is a crucial part of the Ushaan, or traditional Andorian duel to the death using only the ushaan-tor, which an elaborate code calls for in response to any number of precisely defined insults and slights.
Andorian society is non-hierarchical and rather egalitarian. There are no permanent leaders; rather group leaders are chosen by consensus when a leader is necessary to complete some task or deal with outsiders. Nevertheless, until it was folded into the Federation Starfleet, there was a class of Andorian warriors called the Andorian Imperial Guard, bound by a strict code of honor, which defended the chosen leaders and served as the guardians of the Andorian empire.
History
The Andorians discovered interstellar space travel a few hundred years before humans did, and established an interstellar Empire around the turn of the 20th century. The Andorian star system is a close neighbor of the Vulcan star system, and around the 1950s a vicious war broke out between the passionate Andorians and the emotionless Vulcans, and lasted for about 200 years. Finally, the war settled into a kind of cold war and ultimately ended in a lasting peace, when the Andorians and Vulcans recognized their common interests and allied with the Tellarites and the Humans to resist the growing power of the Romulan Star Empire. Eventually these four allies would become the founding members of the United Federation of Planets, in 2161.
Despite their passionate and warlike nature, the Andorians have largely been staunch and loyal supporters of the Federation, and its peaceful, utopian vision of interstellar harmony. A few small factions of Andorians refused to join the Federation however, and remain fiercely independent, hiding out on inhospitable, backwater worlds and occasionally engaging in space piracy.