Noonien Soong's former wife, who helped create Data and who, unknown to herself, was an android duplicate of the original Juliana.
Juliana Tainer had been married to Noonien Soong and had lived with him on Omicron Theta, where she helped build Data and Lore. In Inheritance she met Data while he and the Enterprise-D crew helped save the planet Atrea IV, and she told him about his early life and why she and Soong had deactivated Lore.
Data noticed details in her behavior and discovered that she was an android. A holographic message from Soong explained that the real Juliana had died, and he had built a replacement with her memories. Data chose not to tell her, allowing her to continue her life believing she was human.