Chicago Fire: All the original cast members who left and why

• Chicago Fire has seen many cast members come and go over the years, and considering the popular drama series has been on air for an entire decade, it's hardly surprising. MORE: Chicago Fire stars' low-key weddings: From Jesse Spencer's home nuptials to Kara Killmer's ranch But whatever happened to the original cast members who left the show, and why did they leave? Read on to find out… WATCH: Chicago Fire: Casey say goodbye to Firehouse 51 Jesse Spencer as Lieutenant Matthew Casey Jesse Spencer