In Wrath of Khan, a device is introduced called "Genesis." This device allows the user to take a dead planet or asteroid and rebuild it on a molecular level so that it can support life. The problem is, if you use it on a world which already has life, everything on that planet will be destroyed in favor of the new blueprint. During the climax of the film, Khan, his ship disabled and his crew dead, launches the Genesis device inside of a nebula in order to try and destroy the Enterprise. The Enterprise escapes, and Genesis coalesces the raw materials in the nebula into a new planet, dubbed the Genesis planet. In order to facilitate the Enterprise's escape from the nebula, Spock sacrifices himself by going into the warp core restore the ship's warp drive. His body is deposited on the Genesis planet as the film ends.

In Search for Spock, it's discovered that Spock's thoughts and personality were relayed into McCoy before Spock died, and that his body has been reborn by the restorative energies of the Genesis planet. Kirk takes the Enterprise back to Genesis, where he encounters a Klingon Bird of Prey. As the Klingons swarm onto the ship to take the crew hostage, Kirk sets the Enterprise to self-destruct and beams himself aboard the planet. Ultimately, he comes face to face with the Klingon commander and defeats him (but not before the Klingons kill Kirk's son) as Genesis, proven to be unstable, breaks itself apart. Thus the crew takes command of the Klingon ship and takes it to Vulcan, where Spock's memories and personality are restored.

The fourth film opens as the crew go back to Earth in the Klingon ship. On the way, they receive a message from Starfleet not to approach earth because an alien probe has begun assaulting the planet, and disables any ships that come near. Analyzing the transmission of the probe, Spock determines that the only beings that can answer the call are Humpback Whales, extinct in the 23rd century. So the crew goes back in time to get some whales, and use the cloaking abilities of the Klingon ship to keep themselves hidden.