Even though Mathieu joined a squad with stars such as J.J. Watt, DeAndre Hopkins and Deshaun Watson, it didn't take long for his teammates to take notice of the talented safety who provides leadership on and off the field.
"He's leading guys, pointing guys in the right direction and leading by example," veteran cornerback Johnathan Joseph said of Mathieu taking charge on the field. "His game speaks for itself. He brings guys around him because he has a lot of confidence in his abilities, and I think that rubs off on other guys.
"I think that's the type of guy you need back in the back end on this team."
Several people around the organization describe Mathieu as a "natural leader," noting a commanding presence that emerged the minute he signed with Houston in March. And it's clear that despite the trouble he got into at LSU with his dismissal from the program and 2012 arrest, his ability to guide others has been a staple of his entire football career.
Texans running back Alfred Blue, who played with Mathieu for two seasons at LSU, said the "Honey Badger" is the same player he knew when the pair first played together eight years ago.
"There isn't much of a difference," Blue said. "The same guy he is today, he was back then. The same things he does in the NFL, he did in college. For me, watching him be the same person all these years, it's just a compliment to him.
"People say positive vibes ... it's contagious. His playmaking ability on defense is contagious. He gets the team going, and that's what we need." Texans running back Alfred Blue
"It's just his confidence. His will to win. His will to make plays. People say positive vibes ... it's contagious. His playmaking ability on defense is contagious. He gets the team going and that's what we need."
Mathieu, an All-Pro in 2015, also was thought of highly in Arizona, where he spent his first five NFL seasons before being cut in March. After the Texans signed Mathieu to a one-year, $7 million contract this spring, Houston coach Bill O'Brien said former Cardinals head coach Bruce Arians told him he'd "stand on that table 10 times for Tyrann Mathieu."
"That meant a lot to me," O’Brien said, "and after meeting him, I can see why."
That leadership often comes to the forefront because of the energy Mathieu has on the field -- noticeable even as training camp drags into its third week during a long, hot joint practice with the San Francisco 49ers.
"Tyrann Mathieu plays with a lot of passion," Hopkins said. "That's Tyrann. He's the quietest and chillest guy outside of the football field, but once he's on the field, he's the Honey Badger."
The Texans hope Mathieu -- along with a healthy defensive line -- turn around a defense that struggled under then-coordinator Mike Vrabel last season. In 2016, the Texans had the No. 1 overall defense and ranked second in passing defense, allowing just 201.6 yards per game.
In 2017, lacking a playmaker in the secondary after cornerback A.J. Bouye left in free agency, the passing defense fell to 24th, allowing an average of 237.4 yards per game. Mathieu won't fill Bouye's void directly -- he will start at safety, his natural position -- but O'Brien and defensive coordinator Romeo Crennel have said they would like to eventually move Mathieu around the secondary as he becomes more comfortable in the scheme.
"The D-line wasn't healthy," Mathieu said of last season's Texans defense. "I think that plays a part in how we perform on the back end. Everything goes hand in hand. We'll get a couple of guys back; obviously, like I said, we added some guys in the secondary. It's going to be important for us to kind of get a feel for each other, because we do have a big game Week 1. So, we have to be ready."
And seeing Watt and outside linebacker Whitney Mercilus on the field again during training camp? Mathieu smiles when he thinks about what the group can do if all are healthy this season.
"It takes some stress off," Mathieu said.
Mathieu says he feels right at home in Houston, which was an ideal landing spot for him in free agency in part because of the proximity to his family in Louisiana. On the field, he has been welcomed with open arms, mostly because of his attitude and energy, which could be the spark Houston's secondary needs.
"I've had a lot of guys on the team really support me, really wrap their arms around me and really embrace me as a leader on this team, and I've just gotten here," Mathieu said. "For me, that's a big pat on the back. Obviously, I have a long way to go, but I just want to show these guys every day that I'm going to show up and be ready to work.
"It's all about your attitude, how you approach things," he added. "Obviously, camp is long and it can get tedious sometimes. You get tired of looking at your teammates sometimes, too, but it's a lot of things you have to push through. I think me wanting to be a leader on this team, that's something that I have to make sure I hold myself accountable, as well. Even if your body isn't there every day, I think your attitude and your mindset, you have to be there. That's what I'm going to try to do every day."