"Alien" was a general-purpose term used in the galaxy by humans and even some droids to refer to anyone of a sentient species that was not a human. Sometimes, the term nonhuman was used interchangeably. To the Chiss, the term was used to describe non-Chiss species, as well as by the Kilji to refer to non-Kilji. There existed within both the Galactic Republic and Galactic Empire a set of Unknown Alien protocols that governed official encounters with unknown alien species.
As the Galactic Empire looked down on aliens, it was rare to find nonhumans serving as Imperial officers. Nonhuman species like Wookiees were regarded as animals and exploited as slave labor. The Empire favored humans in its government and military. In addition, the Empire discouraged the learning of alien languages and cultures such as Ithorese, and sought to impose high "Imperial standards" for its citizens.
This pro-human bias was an intentional part of Imperial policy. Imperial propaganda actively supported state-sponsored ethnocentric xenophobia and fear-mongering. To the Empire, aliens were by and large unwelcome within its order, with aliens being seen as "different" and "strange." As such, the Empire treated nonhuman segments of its populations as serfs, slaves, or obstacles needing to be tamed, removed, or ignored. The Empire supported the idea that aliens were untrustworthy—unlike humans—and behind their veneer of innocence lurked a vicious monster. The Imperial propaganda machine was so effective in its message that even near-human species exhibited an inherent distrust towards nonhuman populations.
Nevertheless, some nonhumans were known to occupy lofty roles within the Empire, such as the Chagrian Mas Amedda, who served as the Empire's Grand Vizier, the Chiss Grand Admiral Thrawn, the Pau'an Grand Inquisitor, and four other Inquisitors known as the Seventh Sister, the Fifth Brother, Ninth Sister and the Eighth Brother.
Some fans of grav-ball during the Age of the Empire objected to the presence of alien players on grav-ball teams, feeling that their alien physiognomies gave them an unfair edge over the human players. The Junior Academy of Applied Sciences's athletic director Janus Fhurek attempted to convince his grav-ball center-striker Zare Leonis to remove the AppSci SaberCats' two alien players: the Rodian Frid Kelio and the Aqualish Hench Sina. When Leonis refused, Fhurek unilaterally transferred the alien players to another school. Reflecting on his experiences with Fhurek, Leonis regarded the athletic director as xenophobic.
The Kilji religious species were xenophobic: they viewed beings who did not follow their beliefs—the Kilji way of order and enlightenment—as inferior, and ignored them and treated them badly until they were enlightened to their philosophy. The Kilji ruler, Generalirius Nakirre, allied himself with the Grysk "Jixtus," an alien, who covered all of his body so no one saw a Grysk body or face until he sat at the ancient thrones of the ancient kings of the Chiss planet Csilla.
Aliens first appeared in the 1977 original trilogy film, Star Wars: Episode IV A New Hope. Director George Lucas stated that the Star Wars mythology, beginning with A New Hope, was the first time aliens are shown not as monsters, but simply common characters.