It's a relationship that began when William Gay was a rookie, and Joey Porter was a fourth-year linebacker.
The relationship grew through the years, as Porter was the veteran showing Harrison the ropes of playing the position in the NFL.
And the relationship is even stronger today, as Porter is Harrison's outside linebacker coach and the two are kindred spirits, sharing the same intense love for the game.
"We both have the passion for the game," said Porter. "I was a vocal guy that was going to play that type of way. He is a determined guy who is going to play his kind of way. When you used to put us out there on the field together, we had so much fun doing it.
"There are a lot of different ways people can do their job. He has had a lot of success doing it his way. It was pick your poison on what style of football you liked to watch out there. It's always been good to watch from where he started to where he is now."
Where Harrison is now is the result of hard work, determination and a never say die approach. Harrison entered the NFL as an undrafted rookie free agent and today is the Steelers' all-time sack leader with 79.5 sacks, and 81.5 overall in the NFL.
Porter remembers Harrison's first sack well. Harrison got his first NFL start on Nov. 14, 2004 against the Cleveland Browns after Porter was ejected before the game even started because of a pregame fight. Harrison sacked Browns quarterback Jeff Garcia for a three-yard loss that day for his first sack. And he broke the record this past season, against Cleveland again, when he sacked Cody Kessler for a five-yard loss.
Seeing him get the record-breaking sack meant something special to Porter.
"The coolest thing was watching him go out against Cleveland, where he got the first sack, and watch him break the record against Cleveland," said Porter. "That was cool.
"I still love to watch him play and live through what he is doing. I love to watch him have success. One of the coolest things was watching him break the sack record. We had a talk when his father passed last offseason. He was in a tough spot not knowing if he wanted to play again because it was the first season he was going to take the field without his dad. We sat around and I told him, I don't know what to tell you because that hasn't happened to me. But for him to give up anything isn't in his nature. I asked what would (your dad) want you to do. He knows you love football. You worked so hard. You get four or five more sacks and you will be in the history books."
Porter and Harrison's bond is always on display on game day, especially pregame where the two go through a routine where they are making sure opposing teams know that the linebackers aren't to be messed with.
"It's funny," said Porter. "It allows me to still be part of the game. We mess around and get fired up for the game. Every day I go out there, I think I am about to play. In that brief time in pregame warmups, I get that energy back again. He knows it.
"James and I were messing around one day, getting fired up, us having fun. We get so into it. That is just me not wanting to let the game go and him still in the game. It gets me fired up and gets him fired up too."