The Malkus Artifacts (also known as Instruments of Malkus or Instruments of Power) were four sinister devices designed by the alien known as Aidulac for the mad tyrant, Malkus of the ancient Zalkat Union over 90,000 years ago. Legends claim that Malkus ruled for over 1,000 years using the artifacts. Aidulac designed the artifacts to be completely indestructible and immune to the ravages of time. Indeed, after 90,000 years, only one of the artifacts showed even the smallest damage.
Malkus commissioned Aidulac to grant him four specific powers, and thus she created four black box-like devices, marked only with Malkus' name, that corresponded with the powers he wished: A device that could change weather patterns, to give him power over the elements; a device to manipulate a person's thoughts, for power over the mind; a device that unleashed a deadly adrenal virus, for power over life and death; and a device that projected a powerful force beam, for the power to overcome any enemy. They became the hallmarks of Malkus' rule, as he unleashed the power of the artifacts against any who dared to oppose his rule.
A rebellion eventually brought an end to Malkus' thousand-year reign, and the rebel movement - which subsequently became the Zalkatian government - attempted to destroy the artifacts to prevent their being used again. After this failed, the Zalkatians decided that if the artifacts couldn't be destroyed, they should be spread across space, their locations known to no one. The artifacts were hidden throughout a vast region of the Alpha Quadrant, much of which would later be part of the United Federation of Planets. Malkus' essence was imprisoned within the mind controller, as a means of punishing the tyrant for his crimes. Aidulac was also placed on trial for her part in the creation of the artifacts, but managed to escape and begin a ninety-millennia search to locate the artifacts and find a way to destroy them. (TNG - The Brave and the Bold, Book One novella: The Second Artifact)
The first discovery of the artifacts' existence came in the year 2151, when the crew of the Enterprise discovered a "chronicle" of Malkus' reign on the world Beta Aurigae VII, the former Zalkatian capital. This discovery led to the eventual establishment of Starfleet's General Order 16, which required that any object that matched the artifacts' energy signature be confiscated by Starfleet. (ENT - The Brave and the Bold, Book One short story: "Prelude: Discovery")
The first of the artifacts, the one that inflicted a deadly plague, was discovered in 2266 on the planet Alpha Proxima II. An emergency situation arose as the artifact's discoverer, one Tomasina Laubenthal, unleashed the plague upon the world's population. The situation was resolved, and the artifact recovered, by Commodore Matthew Decker of the USS Constellation and Captain James T. Kirk of the USS Enterprise and their respective Chief medical officers. (TOS - The Brave and the Bold, Book One novella: The First Artifact)
The telekinetic artifact was discovered in 2370 on one of the moons of Bajor by the Bajoran terrorist Orta, who tried to use it to actually align Bajor's moons in order to facilitate an ancient Bajoran prophecy. This situation was resolved by Colonel Kira Nerys of starbase Deep Space 9 and Captain Declan Keogh of the USS Odyssey. (DS9 - The Brave and the Bold, Book One novella: The Second Artifact)
The weather-controlling artifact was discovered in 2371 in the Demilitarized Zone by the Andorian member of the Maquis known as Tharia ch'Ren. Tharia used the artifact in a brutal vendetta against the Maquis' enemies, and was finally stopped by efforts from both members of his own Maquis cell (including former and future Starfleet officer Chakotay and undercover Starfleet officer Tuvok of Vulcan), and Captain Robert DeSoto of the USS Hood. (VOY - The Brave and the Bold, Book Two novella: The Third Artifact)
The final artifact, the mind controller, was discovered in 2376 on the world of Narendra III by a Klingon sculptor named J'lang. This artifact housed Malkus' consciousness, and he summoned all of those that had been imprinted upon the artifacts. It took the combined efforts of the crews of the IKS Gorkon and the USS Enterprise-E to break Malkus' hold over Narendra and deactivate the artifacts. (TNG - The Brave and the Bold, Book Two novella: The Final Artifact)