The Persian Brotherhood of Assassins was the branch of Assassins that operated in Iran. Prior to its foundation, the organization had at least one major predecessor during the Achaemenid Empire: Darius, a man whose assassination of the King of Kings Xerxes I was the first recorded usage of the Hidden Blade in history. It remained active into the 18th century, where its agents sought the Koh-i-Noor and the death of the usurper Nāder Shāh.
In 465 BCE, a Persian man named Darius assassinated the Achaemenid King of Kings Xerxes I who was supported by proto-Templars. His deed became renowned among the later Assassin Brotherhood, for it went down in their history as the earliest recorded usage of the Hidden Blade, their iconic weapon. For this reason, Darius was posthumously honored as one of their predecessors.
In 1050, Hassan-i Sabbāh reorganized the Assassin Brotherhood into a public state based in Alamut, a castle in northern Persia. In 1162, during the reign of Hassan the Younger, an Assassin later known as Al Mualim was sent to the Levant to expand Assassin influence, establishing another branch autonomous from Alamut.
Under the tenure of Al Mualim's successor Altaïr Ibn-La'Ahad, paramount responsibility for the Assassins as a whole rested with him while he led from Masyaf in the Levant. As a consequence, when he later dissolved the state to lay the seeds for the various Assassin Guilds around the world, the original Persian branch was retroactively grouped with the Levantine branch as the Levantine Brotherhood.
In 1747, Salah Bey, the captain of guards for Nāder Shāh assassinated the Iranian ruler and hoped to retrieve his Piece of Eden, the Koh-i-Noor diamond. However, the Koh-i-Noor had already been passed off to Ahmad Shāh Durrānī, an Afghan chief, who therefore became the next target of Salah Bey.