"Mr. Fireman" was born on January 4th (the year of his birth is unknown) somewhere in Jasper Alabama. He lived with his parents until he was 17 years old, when he moved out and began attending college. He remained at college until he was 20 years old when he suddenly went missing. He remained missing for exactly five years when he cousin, nicknamed Mr. Ambulance, discovered him living in a Mcdonald's bathroom. Out of pity, he invited Mr. Fireman to come live with him in his apartment, to which he agreed. The two then began living together and did throughout the duration of the show.
His biological father Bernard Flenderson died when he was a teenager.
He was portrayed as a near-obese man who always wore his firefighting suit, even when he was not working. He also had a radio communication device with him at all times, but he never seemed to use it.
While not his real name, "Mr. Fireman" gave himself this nickname to start a public trend, to be known as "Mr. Fireman: The world's greatest fireman. So great in fact that it only be fitting that he be the true, the one, and the only, 'Mr. Fireman'"
However, his lifestyle was polar opposite of that. His character was a lazy, nearly obese bum who enjoyed nothing more than eating junkfood and watching TV any moment he wasn't in any of his classes.
He was, respectively, a firefighter in training who took classes from his teacher, Buzz Tarco. Although he is technically in class training, he sometimes also gets assigned to the payed portion of his job; "Building cover". As a result, he always refers to his classmates as "co-workers" and to Tarco his "boss". Jonah has an unspecified number of co-workers, with Samuel, Johnson, and Ryan, being the names of the most seen and mentioned ones. The firemen were punished by Tarco on a seemingly regular basis for one reason or another, usually for throwing food-fights in the cafeteria during lunch break, or, on rare occasions, even in the classroom itself. Often times, he is sent to the fire department's ultimate punishment, The Bonus Round. Out of any of the firemen at the department, "Mr. Fireman" was sent to The Bonus Round by far the most often. Ironically, anytime he receives an emergency call, he was able to get the job done somewhat successfully, but otherwise, never got any work done at all. However, he rarely, if ever, responded to any emergency call, as his only job with the department was "building cover", which only involves sitting on top of a building, checking it's surface temperature, and making sure it doesn't burn down.
Despite being a firefighter, he always had a tendency to accidentally set almost anything on fire. One on occasion he even set an airliner lavatory on fire.
In the Season 5 episode "Lenny and Mr. Fireman Break Bad, his character visits his local Mcdonald's (NOTE: This incarnation was before the creation of the fictitious "Ncdonald's") and asks for free food, for no apparent reason, in hopes that they will be generous and fulfill his nonsensical request. The manager refused, but Mr. Fireman continuously pleaded with the manager until he ended up banned from that Mcdonald's for the rest of his life. He remained banned there for the duration of the series. In the 2014 episode "Lenny's Thanksgiving Kerfuffle", which took place over a year later, it was referenced that he was still banned from that Mcdonald's.
His birthday is January 4th, however, the year of his birth is unknown.