Circa 3800 BCE, a Betan philosopher named Landru became concerned that the wars amongst the Betan people would ultimately destroy themselves and the planet. In order to bring peace to the planet, Landru built a sophisticated computer - also named Landru - which "absorbed" members of Betan society, allowing their actions and emotions to be controlled by the computer. Once Landru's influence had spread over the planet, war, disease, crime, fear, and conflict had been eliminated. The computer also assumed automated control of much of the society's technological systems and infrastructure.
A century later, the USS Enterprise was dispatched to Beta III to ascertain the fate of the Archon. The Enterprise crew were likewise confronted by Landru and threatened with absorption. But Captain James T. Kirk was able to deactivate the Landru computer by convincing it that it had destroyed the very society it was supposed to protect, thereby creating a paradox in its programming.
With Landru's influence negated, Captain Kirk left Ensign Christopher Lindstrom and a team of sociologists behind to help guide the Betans in their new freedom. Additionally, the Corps of Engineers sent the USS Lovell to help bring Beta III's necessary automated systems back online; Enterprise chief engineer Montgomery Scott also remained on Beta III to assist them. (TOS episode & Star Trek 9 novelization: The Return of the Archons)
During this period, Landru was briefly reactivated, and attempted to reassert its influence over the Betan populace. The computer was disabled once again by an electromagnetic pulse generated by a blast from an old spatial torpedo which had been salvaged from the Archon a century earlier. Starfleet considered using Beta III as a starship maintenance facility in the 2260s. (SCE - Foundations eBook: Foundations, Book Two)
In the mid-2370s, the Aerie-class starship USS Rook was assigned to an extended sociological re-education program on this planet, under the direction of Doctor Timothy Wess. (Decipher RPG module: Starships)
However, by the year 2380, the Landru-computer had once again reasserted itself over the populace of the planet in spite of all the various Starfleet interventions attempted over the previous century, and it fell to the crew of the USS Cerritos under the command of Captain Carol Freeman to liberate the Betan civilization by reiterating Captain Kirk's original message to the population. In a move unauthorised by Captain Freeman, Ensigns Beckett Mariner and Brad Boimler distributed painting, writing and drawing tools to Betan children to encourage creativity and individual expression. (LD episode: "No Small Parts")
In the Kelvin timeline, by late 2258, the information in the Federation Archives about Beta III listed it as a "barren rock". All information that remained were rumors, including one passed on to James T. Kirk at Starfleet Academy by one of the professors. Cornelius Landru was actually the head of Starfleet's Advanced Research Division in 2167. Landru's, along with the Archon's, mission was to establish one of the first deep space colonies on Beta III that would be regulated by Landru's technology to make the colony thrive.
In reality, Landru's technology was to control the colonists and make Landru a god himself. The Archon and it's crew then tried to stop him but failed when his technology pulled the Archon from the sky. The surviving crew on the ground were then left without means to contact Starfleet. (TOS - The Return of the Archons comics: "Part 1", "Part 2")
In the "mirror universe", the Andorian Imperial Guard conquered Beta III in 2155 on behalf of the Terran Empire. General Thy'lek Shran, when presenting spoils of the invasion to Empress Sato, described the inhabitants as "little more than sheep." (ENT - Mirror Universe novel: Age of the Empress)
- It is unclear what role, if any, Landru played in the history of this mirror Beta III.