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|
Background information Edit
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.