Cleon XII is a recurring character in the Apple TV+ series Foundation. He is the twelfth Emperor of the Genetic Dynasty. At the time of Hari Seldon's arrest and the subsequent founding of the Foundation, he ruled on the middle throne of the Empire as Brother Day, the most powerful. He is capable of being charming but is also prone to volcanic eruptions of anger. Cleon XII is initially portrayed by Lee Pace, first appearing in the episode "The Emperor's Peace". From "The Mathematician's Ghost", he is portrayed by Terrence Mann.
Cleon XII ruled as Brother Day at the time the Foundation was proposed and established. He and the elder Cleon XI helped to educate the young Cleon XIII on the subtleties of ruling the Galactic Empire, along with their aide Demerzel. Cleon XII sat on the middle throne when he met with delegates from Thespis and Anacreon, having to maintain the peace when two Imperial appraisers were caught in the crossfire during their mining dispute.
After the trial of Hari Seldon and Gaal Dornick, he met with Hari and granted him the resources needed to establish the Foundation. However, fearing the consequences of emboldening his followers, he granted them the planet of Terminus, a barren world at the edge of the Galaxy.
After the Star Bridge was destroyed in a terrorist attack, Cleon XII ordered Anacreon and Thespis to be bombed. He had images of the bombings broadcast on Trantor, forcing the ambassadors to watch as members of the diplomatic delegations from both worlds are executed in a show of the Empire's strength. He allows the ambassadors to live, and return to their homeworlds with word of their failures.
In 12,086, Cleon XII saw to the ascension of Cleon XI, with the dying Emperor proclaiming Cleon XII to be the new Brother Dusk. Cleon XIV is presented to Cleon XI as a newborn, and becomes the new Brother Dawn, with Cleon XIII becoming the new Brother Day on the middle throne of the Empire.
In 12,102, the Empire is informed of the death of Proxima Opal, who Cleon XII once helped instal as the head of Luminism. Her death causes a potential crisis for followers of Luminism in the Empire, as a potential successor, Zephyr Halima, champions a return to the Primary Octavo, which considers clones to be lesser beings, as in its belief the soul only cleaves to one body. Dusk proclaims he will travel to to Opal's funeral on the Maiden and address the conclave. However, Day blames Dusk for the problems plaguing the Empire, such as his handling of the Seldon crisis and the bombing of Anacreon and Thespis. He orders him to remain on Trantor, while he travels to the Maiden for Opal's funeral. As Day departs Trantor, Dusk orders Dorwin to head to Terminus and remind the Foundation they are still Imperial citizens.
While Day is away, Dusk introduces Dawn to the pastime of hunting Ghillie raptors, which are difficult to see because they blend in with the environment. Dusk is impressed to see that Dawn has caught three, the same as his own record. He later introduces Dawn to the sexual pleasures of the Gossamer Court. Before the memories of the woman Dawn chose are to be wiped, Dusk meets with her, and learns that he did not sleep with her. He orders the woman to tell him everything Dawn said to him.
- Season One