PHOENIX — Yes, Rob Gronkowski likes kittens.

Yes, Rob Gronkowski owns a party bus in which his family members and friends can tailgate before and after every game.

Yes, Rob Gronkowski bobs through the New England Patriots locker room with a smile on his face. Every day.

As Tom Brady said Thursday of the fifth-year tight end, “I don’t think he’s ever had a bad day in his life. He always seems to have a great time.”

But don’t mistake Gronkowski’s off-field personality for his on-field persona.

“Avoid getting him angry,” said Patriots defensive end Rob Ninkovich. “He is a very strong man.”

Just ask Sergio Brown, the defensive back for the Indianapolis Colts. Known for his trash talking, Brown got on Gronkowski’s bad side during the Patriots’ 42-20 win on Nov. 16 – and Gronkowski blocked him into the stands on a play. Or, as Gronkowski said, “I threw him out of the club.”

“He’s a happy, fun guy,” Ninkovich said. “But on the field he’s pretty intense.”

And a lot more dedicated to football than people give him credit for.

‘HE’S A SMART FOOTBALL PLAYER’

Since the Patriots drafted Gronkowski out of the University of Arizona with the 42nd pick of the 2010 draft, he has become one of the NFL’s ultimate offensive weapons. He is the only tight end in NFL history to have four seasons with at least 10 touchdown catches. He has caught 59 touchdown passes in his career, including playoff games.

And he will be the Patriots’ most potent offensive threat, other than Tom Brady, when New England faces the Seattle Seahawks in the Super Bowl on Sunday.

But he’s also been videotaped partying, or dancing, or simply goofing around with his brothers: Gordie, Dan and Chris. That gives many the impression that Gronkowski is simply a 6-foot-6, 265-pound frat boy.

The Patriots know better.

“You know, Rob’s a smart football player,” said Patriots coach Bill Belichick. “He understands a lot of things about the game, not just the X’s and O’s, but also how he’s getting matched up individually and what our opponents are trying to do given the situation. He’s worked hard on that, he’s seen a lot of different coverages, or getting jammed at the line, you know, whatever teams try to do.

“He’s a good football player. He’s a smart football player.”

‘THAT’S WHAT FOOTBALL IS ABOUT’

The Seahawks know this. They have one of the most feared defenses in football, led by the vaunted Legion of Boom secondary.

Strong safety Kam Chancellor likely will cover Gronkowski, and players on both teams are looking forward to that matchup.

“It’s going to be loud, I’m sure it’s going to be loud,” said Seattle cornerback Richard Sherman. “Two big, strong men. I think that’s what football is about. I think a lot of people are looking forward to that.”

Maybe even Jeremy Lane. After all, he’s the third-year Seattle cornerback who said of Gronkowski, “I actually don’t think he’s that good.” Gronkowski wouldn’t get into it with Lane, simply saying that comment might tick him off.

But Pete Carroll, the Seahawks’ coach, knows his team faces a challenge.

“He’s going to catch his passes,” Carroll said. “We can’t let him control the game.”

The last time the Patriots advanced to the Super Bowl, in 2012, Gronkowski was a mere footnote. Oh, he had a great season, with 90 catches for over 1,300 yards and 17 touchdowns, but he injured an ankle in the AFC championship game and was hobbled against the New York Giants.

He caught only two passes for 26 yards in New England’s 21-17 loss.

This time?

“It’s a lot better,” Gronkowski said. “I remember a few years ago being here, every single question (was) about my ankle. Every 4 seconds somebody asked me about my ankle. It’s cool to come here, just chill, just worry about the Seattle Seahawks. It’s awesome.”

That he’s simply healthy again is good enough for Gronkowski.

He missed five games in 2012 with a broken arm, then missed the first six games in 2013 when it wasn’t healing properly. He returned, then blew out his right knee on a tackle by T.J. Ward on Dec. 8 and missed the rest of that season.

This year, the Patriots brought him along slowly, with only 13 catches in the first four games. He finished with 82.

JUST HAVING FUN? ‘PRETTY FUNNY’

There were times, he said Thursday, that he wasn’t sure he would return to his form.

“But when you start the rehab process that you’re going through, you’re getting stronger every day, you have the training staff that’s motivating you, you talk to other guys, players that have been through situations that you’ve been through that are successful again,” he said. “Once you hit a point where you feel like you’re gaining, you’re getting back at it, that’s when you gain all the positive energy and positive thoughts.

“You just think in your head that I can be back better than ever and better and stronger. In that case, I feel like I have, for sure.”

He has certainly put in the work, something a lot of people don’t see.

“I mean I can tell you this, it’s top-of-the-line conditioning, top-of-the-line weight training, top-of-the-line preparation of getting your body where it needs to be,” Gronkowski said of his workout regimen.

The perception that he’s just having fun, he said, is wrong.

“People, sometimes I feel, like just look at me like I just go out 24/7,” he said. “It’s pretty funny. I just laugh it off, but really … throughout the whole week many times during the season I don’t even step foot out of my house. I just chill and make sure I’m taking care of my body and making sure I’m doing what’s right to get ready for the next day at practice.

“As I’m maturing more in this league, I feel like football just keeps getting more and more important to me.”

The fun, he said, will come with the success.

“You’ve got to have fun, there’s definitely time to be serious and definitely time to have fun,” he said.

“When you go into meetings, you go out to practice, I put those things first. All the time. I put my football first, my job first. You want to go in, make an impact for your teammates. You want to show how it’s done on the field, you want to go out and practice hard so that they know what it takes to get to the next level.

“I feel like if you work hard, you deserve stuff to go out and have a little fun.”