Twelfth, once known as Sinner Twelt, is the head of the September Institute. He uses the Divine Voice to influence Kobus and Loyalty and install assets in Lux Vox Data Research Center and Vox, according to the direction of Ibex and the Liberty and Discovery Automaticorps.
After Service II pushed out Service, Twelt made deals with outsiders like Maryland and Ibex and further corporate interests to create the September Institute and expand Mode City's entertainment and commercial sectors. When the burgeoning worker's movement criticized him for this, he bought or silenced any opposition.
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He is more interested in his own agenda than Ibex's grand plan.
Some time after the Golden War, after Maryland started to get sick, the two of them quarreled over the future of the Institute, leading her to quit and him to take the position of Provost Regent. At some point, he also seems to have taken control of Ibex's paramilitary installation on September, the Tzadik unit, without approval, and used it to keep September's cloning program under wraps.
He sent the crucial message inviting Rigour to September. In "The Storm Over September" he attempts to assert control over Rigour as it wakes, but this no doubt futile attempt is cut short by Paisley killing him.