Initially thought by the Vault 76 overseer to be a human that had sheltered themselves away at the apex of the Top of the World ski resort and thus survived the ravages of the Scorched Plague, the resident that eventually makes their way to the observation deck finds that Rose is not what the overseer had in mind.
Rose is a heavily modified Miss Nanny and self-proclaimed leader of the Appalachian raider gangs. As one of the few cognizant remnants of Appalachia's raider gangs, she sends the Vault 76 resident on various tasks both for practical purposes, as well as her own cruel amusement.
Her behavior and voice are based on that of long-deceased raider Rosalynn Jeffries, the mistress of former Cutthroats leader and now infected, David Thorpe. Her exterior has shown many signs of customization, such as a scrap metal 'mohawk', wrapped chains, and various 'tattoos' painted on her chassis.
Once Signal Strength is completed, the range of her personal radio station is expanded. Still within the Top of the World, she offers tips of dubious usefulness, canned recruitment drives, and stories that give greater insight into the worldview of the raiders that once terrorized Appalachia.
In Top of the World, a holotape recording between David Thorpe and Rosalynn Jeffries can be found. In it, Rosalynn speaks in a mock robotic voice after David orders her around, to which he replies stating she is not a robot. Ironically, Rosalynn's behavior and voice are later used to create Rose.
If one examines Rose's idle animations, she will seemingly inject Psycho into her own robotic chassis. It is unclear if she is genuinely affected by these chems, or if it is instead a programmed response.