Used copy in ruff shape
The first edition of Galaxy Guide 4: Alien Races is a supplement to Star Wars: The Roleplaying Game written by Troy Denning and published by West End Games in 1989. It was revised into a second edition in 1994.
From an in-universe perspective, the book is supposed to be made up of excerpts from the Catalog of Intelligent Life in the Galaxy by an Imperial sentientologist named Obo Rin, who was commissioned by Darth Vader to catalog the intelligent species of the galaxy. The introduction consisted of Imperial communiqués giving an in-universe look at the production of the Catalog.
While many of these species did appear in the original trilogy, some were invented for the game. The background information for several of the alien races who had appeared on screen was also invented for the game. Many of the new species and backgrounds were used in later works in the Expanded Universe with little modification. However, some retcons are needed to bring Galaxy Guide 4 in line with the prequel-era Expanded Universe. The most common retcons necessary are those where a species described as having its first contact with the Galactic Empire are shown in later works to have some contact with the Galactic Republic. Since Obo Rin is said in the text to be an unreliable source with an Imperial bias, these retcons are usually made by blaming inaccuracies on deliberate Imperial propaganda and misinformation.