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Frederick was married to Shannon Rivers, the voice actress of the Mistress of Mystery. To help her prepare for her role in the upcoming Silver Shroud television show, he constructed a training room in their secret basement and installed a custom-built RobCo mainframe that he bought from RobCo after the DIA canceled the project it was built for.
After the war, he and was wife adopted multiple orphaned girls. They later founded the Order of Mysteries to help Appalachia. Frederick was its only male member but wasn't ranked and was their sole technical specialist. He designed many of the tools and clothing based on those used by the Mistress of Mystery. He also had began looking into applying Kent Connolly's idea of ballistic weave to help protect the members. He later created a fabrication machine to automate the creation and repair of the equipment so he could have time to work on new projects.
He reprogrammed the computer system from training his wife to supporting the Order by automating initiation, mentor assignments, and mission assignments. He maintained the computer system, now called Cryptos along with Rachel West and Janet Tyler, who mostly took over its programming while Frederick continued to tinker.
Frederick Rivers is only mentioned in Fallout 76.
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