Victoria starts as a side character in the Twilight series but, in Eclipse, she turns out to be a much smarter and more ominous villain than the Cullens and Bella first gave her credit for. She creates a vampire army to kill Bella, but as a common enemy of the Cullens and werewolves, she brings about their alliance, which leads to her ultimate defeat. So, in a way, her evilness does good in the end. Despite all her feral vengefulness, she could be seen as a tragic character, because she seeks revenge out of love for her mate James, who was killed by the Cullens in Twilight. On the other hand, she uses her companion Reilly to carry out her plan and sacrifices him easily in an attempt to save her own skin.
Reilly believes that Victoria loves him and so he risks his life for her. His loyalty to her is similar to the loyalty Jasper paid to Maria, his creator, who also manipulated his emotions toward her to get what she wanted.
Bree is a newborn vampire, created by Victoria for her army. She surrenders in the fight, but is killed by the Volturi. She serves as a mirror image for Bella to see what she could become after her transformation.