Cynthia is a Nannybot developed by Vault-Tec. The nannybots were created by Vault-Tec specifically to be a competitor to RobCo's Mr. Handy line. They were more advanced and had a more attractive design, and they were to hit the consumer market just a month after the bombs dropped. As such, most are languishing having never been activated in the factory in which they were made. Besides the ones that inhabited Vault 49, the only other ones that existed were those that were used as demonstration pieces at showroom floors across the country or in certain Vault-Tec offices.

Cynthia and Donnie had a particular amount of chemistry which resulted in her being his primary caretaker within the vault (a typical development between the nannybots and their wards.)