Cleon XIII is a recurring character in the Apple TV+ series Foundation. He is the thirteenth Emperor of the Genetic Dynasty. At the time of Hari Seldon's arrest and the subsequent founding of the Foundation, he was a young child as Brother Dawn, the most junior of the three Emperors. After the accession of Cleon XI, he took the middle throne and became Brother Day. Cleon XIII is initially portrayed by Cooper Carter, first appearing in the episode "The Emperor's Peace". In "The Mathematician's Ghost", he is subsequently portrayed by Lee Pace as an adult.
The young Cleon XIII is educated on the subtleties of statecraft by his older "brothers", Day and Dusk, as well as the Imperial aide, Demerzel. The intuitive young boy notices the hateful feud between Anacreon and Thespis.
In 12,086 Era Imperial, Cleon XIII ascended to the position of Brother Day upon the ascension of Cleon XI. Cleon XIV is presented to Cleon XI as a newborn, and becomes the new Brother Dawn, with Cleon XII becoming the new Brother Dusk.
In 12,102, Cleon XIII is spending personal time with a woman from the Gossamer Court, and dares her to try to touch him past his personal forcefield. During the passionate moment, he is interrupted by Demerzel, who informs him of the crisis begun by the death of Proxima Opal, and the possible accession of Zephyr Halima, who seeks a return to the Primary Octavo, which would jeopardize the loyalty of Luminists towards the Empire. Day and Dusk discuss the increase in religious fervor across the Galaxy, along with the insurgencies on Trantor, and the destruction of a comm buoy in the Arcturus Sector, and wonder if Hari Seldon's predictions are truly coming to fruition. With the problems rearing themselves throughout the Empire, Day proclaims that he will go to Opal's funeral in the place of Dusk, blaming the older clone for the handling of the Seldon situation and the bombings of Anacreon and Thespis.
Cleon XIII becomes the first Emperor since Cleon I to leave Trantor, and discusses the situation within Luminism with Demerzel on their way to the Maiden, discussing her own Luminist faith in spite of her robotic nature. Arriving at the Salt Palace, the Emperor is greeted solely by Halima, who petitioned the Ring of Zephyrs to receive him in such a manner. He meets with Ambassador Thanwall and Zephyr Gilat, promising to build a moon-wide desalination system in honor of Gilat's raising to Proxima. Gilat announces the plan at Opal's funeral, but Halima delivers a stirring speech subtly criticizing the Emperor, enhancing her chances at becoming the next Proxima.
As a means to get a win over Halima, Cleon XIII decides he will walk the Spiral and allow his fate to be decided by the Triple Goddesses. Before walking the spiral, he is told by Demerzel the rules for this, such as no inorganic equipment and the rules for assistance in the Spiral, as well as how your fate is decided. Cleon XIII walks the spiral and meets someone along the way who offers him insight into the Spiral and their homeworld. This journey impacts Zephyr Halima as well as his Demerzel.
- Season One