Dr. Robert Viadro was a follower of Rambaldi.
Dr. Viadro was seen walking to the door of his house after Lauren Reed knocked and he answered. She suddenly pointed a gun in his face and started asking him questions regarding something called The Passenger. Viadro managed to fend off Lauren by tripping her and quickly ran to his panic room. Just as the doors were about to seal themselves, Lauren got inside and locked herself in with Viadro.
Lauren began to torture Viadro, demanding that he tell her who The Passenger was before Sydney and Vaughn broke into the panic room, which would confirm Sydney's suspicion of Lauren being the mole within the CIA. After using her brutal methods, Viadro gave her the CD containing the information regarding The Passenger.
When Vaughn and Sydney broke into the room, Lauren was gone and Viadro seemed to be in a state of delirium, rambling how he "betrayed her". When Sydney arrived, he recognizd her from the prophecy and grabbed her gun, pointing it at her and saying she won't hurt her. Vaughn was forced to shoot and kill Viadro before he killed Sydney.