Jeremiah joined the police in 873, and by 880 had become deputy chief of his district. When Police Chief Xander retired in 892, he was one of the top two candidates for the position, and narrowly lost to Mufasa, a deputy from another district. When Mufasa became Police Commissioner in 905, and moved to First Village (where InterVil was headquartered), Jeremiah was appointed as the new chief of the Tonad PD.
In 904, when the surname law was passed, his family chose the name "Masonjar" because several members of the family were glassmiths who specialized in making mason jars, while several other relatives used mason jars in their own work, canning various foods and beverages. (The term "Mason jar" derives from the name of its inventor on Earth, nearly a century and a half before The Land was created. However, when Landian glassmiths first developed the style of jar sometime in this world's second century, they chose to give it that name, rather than something more generic. The name was reportedly learned via their subword sense.)