Lieutenant Junior Grade Sharon "Boomer" Valerii is a Cylon sleeper agent programmed with false memories of being raised in the mining colony Troy by parents Katherine and Abraham Valerii, who supposedly died in an accident that wiped out the colony population. Before the mini-series, Boomer and Galen Tyrol are romantically involved, which is against military protocol due to their ranks. Her programming leads her to black out and sabotage the "Galactica" on several occasions, which Tyrol unwittingly abets by hiding evidence implicating her. In "Kobol's Last Gleaming", Commander Adama sends Boomer on a mission to destroy the Cylon basestar orbiting Kobol; and after her return, she shoots Adama twice in the chest, putting him in a coma and revealing her nature to the crew.