Casey left the series during its 200th episode in Season 10. He moved to Portland, Oregon , to become the legal guardian of his late best friend's sons.
: As the Captain of Truck 81, Casey was defined by his unwavering moral compass and leadership. Matt Casey John Magnum
Spencer’s decision to leave the show in 2021 (during the show’s 10th season) sent shockwaves through the fanbase. His departure was written as a move to Oregon to raise his late best friend’s children—a storyline that perfectly encapsulated Casey’s selfless nature. It was a rare moment in television where a character’s exit amplified their heroic status rather than diminishing it. Casey left the series during its 200th episode in Season 10
When a wildfire threatens the naval base at Pearl Harbor, the Chicago Fire Department’s expert in wildland-urban interface, Matt Casey, is dispatched to Hawaii. There, he meets John "Thomas" Magnum, a security consultant who suspects the fire was set to cover up a theft of military hardware. Spencer’s decision to leave the show in 2021
Thus, might not be a person, but a title : "The Heavy-Hitting John Doe Firefighter from Chicago."