Capella IV was the inhabited fourth planet orbiting the primary Capella. The planet was located close to the Klingon-Federation border. It was the homeworld of the Capellans, a pre-warp humanoid species, as well as the Capellan flower and the Capellan power-cat.
In the mid-23rd century, Capella IV was valued by both the Federation and the Klingons for its rich deposits of topaline. (TOS: "Friday's Child"; TAS: "How Sharper Than a Serpent's Tooth", "The Counter-Clock Incident")
In 2267, the planet served as a pawn in the Federation-Klingon Cold War, during a trade dispute between the Klingons and the Federation over topaline mining rights. The crew of the USS Enterprise was able to secure the rights for the Federation. (TOS: "Friday's Child")
In 2293, the location of Capella in the Milky Way Galaxy was labeled in a star chart that was in Captain James T. Kirk's quarters aboard the USS Enterprise-A. (Star Trek VI: The Undiscovered Country, okudagram)
Capella IV was given a "face lift" for the 2006 remastered version of "Friday's Child", with a digital planet replacing the stock footage from the classic episode.
According to Star Trek: Star Charts (pp. 33, 37, & 47), Capella IV (Alpha Aurigae IV) was located in or near Federation space. Capella IV was ruled by the Ten Tribes of Capella, and was established as a protectorate of the Federation in 2267. The dominant species were the humanoid Capelians. In 2378, there were an estimated 160,000 Capellans living on the planet. A major attraction of the planet was the tomb of Leonard James Akaar.