Sharon "Boomer" Valerii is a copy of the humanoid Cylon model Number Eight who is initially planted as a "sleeper" agent in the Colonial Fleet. She is unaware of her Cylon nature and serves for two years as Lieutenant Valerii on Galactica, where she is assigned as a Starfury pilot and also engaged in a secret relationship with Chief Tyrol. After the Axis attack, her underlying programming repeatedly emerges which leads her to unconscious acts of sabotage. Growing confusion about her true self result in a deep depression and a failed suicide attempt. After Valerii returns from a successful mission to destroy a Cylon basestar, she shoots Commander William Adama in the chest, wounding him critically. She is incarcerated in the brig and soon afterward is executed by Maiev Shadowsong in Camp Oria.

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