Behind the scenesEdit
The Rigellians appeared unnamed in Star Trek: The Motion Picture, their only canonical appearance so far, but have been mentioned in multiple Star Trek series. The information on their biology and evolution comes from designer Robert Fletcher.
In Star Trek, the Rigel system is also home to a savage humanoid species known as the Kalar from Rigel VII, making it possible that the information about Rigellian blood being similar to Vulcans (from "Journey to Babel") and/or their being susceptible to the Romulan disease (as mentioned in Deep Space Nine) actually refers to them. Apparently human characters on episodes "Shore Leave" and "Wolf in the Fold" have been identified as native to Rigel II and Rigel IV respectively, indicating that there are human colonies on these worlds. Rigel X, as seen on Star Trek: Enterprise, is inhabited by an extremely diverse multi-species community. Rigel XII is a scarcely-habited mining colony, as seen in "Mudd's Women".
To make matters more complicated, a humanoid species seen on later Star Trek: Enterprise has been identified as Rigellians, despite the fact that they look very dissimilar to the chelonian creatures from The Motion Picture. It is possible that these represent an immigrant species which was believed to be native Rigellians in the 22nd century and the system was later reclaimed by the chelonians, but this is just speculation. It is also possible that they represent a different native Rigellian species, or even a different ethnic group or gender which belongs to the same species as the reptilian Rigellians. Dr. Phlox once mentioned the Rigellians as a species with four or five genders, giving support to this idea.
In the Star Trek Expanded Universe, the Rigellians are referred to as the Chelons, from Rigel III. According to Memory Beta there are six native species to the Rigel system: the Chelons or Chelarians, the human-like Rigelians (Kalar warriors) from Rigel VII, the Enterprise Rigelians, a race of Vulcanoids from Rigel V (being the ones referred to in "Journey to Babel"), a rat-like species from Rigel IV and a silver-skinned humanoid species also from Rigel IV.
The Saurian action figure produced by Mego was incorrectly marketed as a Rigellian.