The Whale Probe is the non-living main antagonist in Star Trek IV: The Voyage Home.
The Whale Probe had been built by a race of cetaceans in a distant corner of the galaxy about half a million years ago in order to seek out and make contact with life forms - mainly cetaceans - on other worlds. The Probe traveled the galaxy, making contact with numerous other life forms, including humpback whales on Earth.
A little over 300,000 years after the Probe's launch the Probe encountered a hostile species, possibly the Borg. This species, which Enterprise-A CMO Leonard McCoy called "Super Klingons" attacked and severely damaged the Probe. With a large part of its crystalline memory destroyed, the Probe was left with large gaps in its memory after it healed itself.
The probe visited Earth in 2286 after losing contact with the humpback whales. Dwarfing a Federation Miranda-class starship and Earth's Spacedock, the Whale Probe was cylindrical in shape, and carried a small sphere at the front, physically detached from the Probe, but connected by an energy beam. The sphere's purpose was as a communication device, amplifying the Probe's broadcast of its calls to enormous levels, impacting on power systems and exospheres.
In comparison with the Earth Spacedock it passed by at rather close range, the Whale Probe's estimated length was in the vicinity of 70 kilometers – one of the largest space vessels ever encountered by Starfleet. First Contact with the probe by a Federation starship was made by the USS Saratoga while patrolling the Neutral Zone. The Saratoga was disabled by the probe's powerful communication, as were at least seven other vessels along the probe's route to Earth, including the starships USS Yorktown and USS Shepard, and two Klingon vessels. USS Saratoga's scan analysis after disabling Earth Spacedock and the prototype USS Excelsior, the Probe settled over the planet, directing its communications attempts towards its oceans. When it received no response, the Probe began vaporizing Earth's oceans, creating an impenetrable cloud cover over the planet, causing surface temperatures to plummet rapidly.
The Federation President was forced to send out a planetary distress signal, which was picked up by Admiral Kirk, aboard the "HMS Bounty", a captured Klingon Bird-of-Prey. Spock, also on board, quickly established that the probe's call was intended for the extinct cetacean species of humpback whale; Spock theorized that some other species had once been in contact with whales, and had sent the probe after the species went extinct to find out why they had lost contact. Since destroying the probe was impossible, and they would be unable to communicate with the probe itself due to their ignorance of the whale "language" even if they could duplicate the sounds, Kirk determined that the only way to stop the probe was to find some humpbacks who could answer it.
Consequently, the Bounty was taken into the past via the slingshot effect, and successfully retrieved two of the species from 1986. Returning to Earth, the two whales were able to respond to the probe's call, and it departed for an unknown destination, restoring power to the vessels it disabled along the way.
A year later the Enterprise-A encountered the Probe again during a joint Federation-Romulan archaeological mission. This time Spock was able to figure out how to communicate with the Probe in what the Probe considered to be the true language. This led the Probe to grab the Enterprise and a Romulan warbird in its tractor beam and race back to its homeworld.
Arriving home the Probe learned that the "Super Klingons" it had encountered earlier had attacked its creators home star system. After this hostile race caused a second ice age on the homeworld, the creators smashed their moon and used the rubble to construct a fleet of starships, and evacuated their homeworld.
Spock was able to open a dialog with the Probe, and helped the Probe reconstruct its memory to fill in the gaps from the aftermath of the earlier attack. The Probe finally realized that humanoid life - which it had considered as little more than mites - were worthy of communication. Thanks to Spock, the Probe learned that it must speak softly to mites or it would damage their technology and the mites would think the Probe to be hostile.
The Probe then returned the Enterprise and the Romulan warbird to the Alpha Quadrant before departing. On the far side of the galaxy the Probe encountered a star system that was teeming with humanoid life, and sent a message to them, asking if they wanted to talk.
- The whale probe had indeed caused a lot of damage, but the true main antagonists of Star Trek IV were 20th Century Humans. Humans hunted the Humpback Whale until the species extinction which prompted the Probe to come to Earth to find out why they lost contact with the whales.