The league is full of many colorful personalities that are on display every Sunday during football season.
When the idea of a television series came about to showcase an NFL team during an entire training camp, the characters behind the helmets became more even more visible.
Sometimes it is a megastar that grabs the Hard Knocks spotlight, but often times it can be a little-known player on the roster bubble who captures the attention of viewers.
Here are the five most interesting characters to ever appear on the Hard Knocks series.
Putting the wife of Brodie Croyle on a list like this was a tough decision.
Kelli Croyle was the 2005 Junior Miss America winner, and she makes this list way ahead of her husband.
In the end, her adorable Southern drawl, and her other "talents" give Kelli Croyle enough juice to crack the top five.
Terrell Owens was the most charismatic player on "America's Team" during his time with the Cowboys.
Owens was his typical self during Dallas' second run on Hard Knocks while he created his own shirts and yucked it up with coach Wade Phillips.
Say what you want about his attitude and talent, but there is no doubt that Owens was one of the more memorable personalities to appear on the show.
Jared Allen is one of the most colorful personalities in the the NFL. His four episodes on Hard Knocks were no different.
Allen was a featured player on the show, and was quite amusing while wearing snakeskin boots and riding around in a Cadillac with bullhorns on the hood.
His teammate Boomer Grigsby was highly entertaining as well. The duo always seemed to be together stirring up trouble.
Grigsby was making the transition from linebacker to fullback, and he managed to find his way in front of the camera for much of the show.
The outspoken head coach has always had a knack for amazing soundbites, and Rex Ryan saved his best for Hard Knocks.
Ryan was addressing his team in front of cameras after a tough preseason loss, and when he finished his tirade, he took a deep breath and possibly uttered the most famous six words in the show's history.
"LETS GO GET SOME G--D--- SNACKS!"
This, along with the many other entertaining antics, put Rex Ryan at a respectable second on this list.
Chad Ochocinco went to McDonald's daily and spent the bulk of his time on the Bengals version of Hard Knocks hamming up for HBO's cameras.
The entertaining receiver created a variety of catch phrases, including telling opposing cornerbacks that they were about to "kiss the baby."
His 3.5 million twitter followers know how entertaining Ochocinco can be.
Miami signed the former Oregon State Beaver to help a young receiving corps, and his brash off-field antics will help attract some viewers to the Miami Dolphins' Hard Knocks episodes.