Firefighter Randy "Mouch" McHolland

Firefighter Randall "Mouch" McHolland, Truck 81 (recurring previously; season 2–present). Another of 81's more senior firefighters, Mouch is the de facto "legal advisor" of 51 and is their union representative. His wife is Chicago PD Sergeant Trudy Platt (Amy Morton), who also appears in Chicago P.D., whom he meets and marries during the series.