Caprica Six
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Caprica Six is a title given to the Model Six Cylon whose mission it was to manipulate Gauis Baltar into undermining COlonial defenses. After her death and 'rebirth' (through download), she is regarded as something of a celebrity among the Cylons, even other Six models.
Interestingly enough, she immediately begins to hallucinate her own 'Gauis' who talks to her, much like how the real Gauis Baltar has a 'Six' that talks to him. Later, Caprica Six is given the task of helping the reborn Galactica-version of Sharon Valerii readjust to living on Caprica and dealing with the fact that she is a Cylon agent. (Downloaded)