Boomer was the first Eight to serve aboard Galactica. As a Cylon sleeper agent, she was unaware that she was not human or of her programming to sabotage the ship. She was in a relationship with Chief Tyrol, and the two of them had plans to leave the service and start a family before the second Cylon attack. When she begins to suspect that she might be a Cylon, she attempted to eat her gun, but misses her brain and later ends up shooting Commander Adama against her will when her programing asserts itself. Afterwards, she is horrified at what she has done, because she loved Adama like a father and hates herself for it. Callie shoots her out of petty jealousy because she loves the Chief. For this, Callie is given thirty days in the brig for illegal discharge of a firearm.
Before she is resurrected, she experiences a vivid dream
about her being the true Sharon Valerii, a human whom the Cylons used to make all the Eight models.
On New Caprica, when Callie is under arrest, Boomer visits her to tell her that she forgives her and wishes her, Tyrol and their son all the best. Callie replies, "How many times do I have to kill you?" demonstrating that she hasn't forgiven Boomer for having been involved with Galen.
As the living definition of a head-frak, in the last season she switches sides so often, it's hard to know what ship to expect her on. In the end, though she gives Hera back to Athena, who shoots her, knowing she still can't be trusted. But she died doing the right thing and knowing how it was going to end for her. And she seemed content with it.