Stewart Greenberg was a security guard on board the Excalibur. Greenberg was shot and wounded protecting Max Eilerson when some of the crew became possessed by mind-altering aliens. He was later pronounced paralyzed and brain-dead by Dr. Sarah Chambers. Max was greatly affected by the sacrifice of Greenburg, stating that nobody had ever saved his life like that before. After the crisis, Gideon dictated a message to Greenberg's mother, telling her of her son's bravery and self-sacrifice.