Rigel IV was the inhabited fourth planet of the Rigel system, less than ninety light years away from Earth. (ENT: "Two Days and Two Nights") The planet was the homeworld to the Rigel IV natives, including the Hill People, and had deposits of boridium and murinite. (TOS: "Wolf in the Fold")
In 2266, the Redjac entity possessed Hengist, a native of Rigel IV, and killed several women on the planet. He was never caught and was only known as "Beratis". On Argelius II, Redjac committed a murder with a knife from Rigel IV's Argus River region. (TOS: "Wolf in the Fold")
In the 24th century, a brilliant astronomer with a fondness for the Betazoid Ambassador Lwaxana Troi resided on Rigel IV. He named a star after Lwaxana, or so she claimed in 2367. (TNG: "Half a Life")
Rigel IV was also the site of a pergium refinery. During the Dominion War, a shipment of pergium en route to Rigel IV from the Sappora system had been destroyed by the Jem'Hadar. (DS9: "Prodigal Daughter")
|Rigel II • Rigel III • Rigel IV • Rigel V • Rigel VI • Rigel VII • Rigel X • Rigel XII • An asteroid belt|
|See also: • Beta Rigel • Rigel Beta|
Background information Edit
This planet was only mentioned in dialogue.
Evidence for the statement that Rigel IV is less than ninety light years from Earth is specifically that, in "Two Days and Two Nights", the NX-class Enterprise sets a milestone several months after undertaking a mission to Rigel X (which it visits in ENT pilot episode "Broken Bow") by becoming the first Earth ship to travel ninety light years away from the Sol system.
A question, which was not seen on screen, from Spock's memory test in Star Trek IV: The Voyage Home established that Rigel IV at one point signed a peace treaty with Argus. The treaty was important because it set a legal precedent that, "All beings may not be created equal yet shall be given equal opportunity and treatment under the law." 
According to Star Trek: Star Charts (pp. 52, 59, "United Federation of Planets I"), Rigel IV, also known as Beta Rigel IV, was an M-class planet. The planet was a member planet of both the United Rigel Colonies and the United Federation of Planets. Rigel IV was admitted, along with the United Rigel Colonies, to the Federation in 2202.