TEMPE, Ariz. (AP) - Darnell Dockett finally has the contract he feels he deserves.

The Arizona Cardinals announced on Wednesday that they have signed the two-time Pro Bowl defensive tackle to a four-year extension worth up to $48 million with $30 million guaranteed.

Dockett had two years left on his previous contract, so the new deal runs through the 2015 season. A third-round draft pick out of Florida State in 2004, Dockett has developed into one of the best at his position entering his seventh NFL season as the high-spirited leader of the Arizona defense.

"We are very fortunate to have a player of Darnell's ability," general manager Rod Graves said, "and I think even more so his passion for the game."

Dockett has 26 career sacks, 20 in the last three seasons. His seven sacks last year were the most for an NFL defensive tackle. His three sacks against the Pittsburgh Steelers two seasons ago tied Reggie White's Super Bowl record.

Dockett has started all but one game since coming to the NFL and enters the season with 81 consecutive starts.

The extension follows a change in Dockett's approach to the contract issue. As long as two years ago, he has made it clear he believed he deserved a bigger contract. Last year, he sat out minicamp with a so-called sore hamstring. But he was there on time for the 2009 training camp and has not missed any workouts since, leaving the contract issues to agent Drew Rosenhaus.

Not that Dockett's free spirit still doesn't get the best of him at times. This summer, he made an ill-advised streaming Internet video taking a shower to win a bit, but promptly made a public apology.

"The thing that has really made it so apparent that we wanted to get this deal done was his growth as a player and as a person," coach Ken Whisenhunt said. "Where he sits right now in front of you guys, after having a couple of Pro Bowls, after how he works with our team, it's a little bit different than he was almost four years ago when we started this thing."

Eleven days before Arizona's season opener, he sat at a news conference on Wednesday to announce his new contract, Graves on one side, Whisenhunt on the other.

"I know a lot of people probably thought I wasn't going to come to training camp," Dockett said. "I made a commitment to players that I was going to be there, like Joey Porter. I told him I would be there and I didn't want to let him down. Once I put my helmet on and shoulder pads, I can honestly tell you I really didn't think about contract. I just focused on football and believed they could get it done."

For the quick, punishing 6-foot-4, 290-pound tackle, the new deal is a rich testament to his ability to overcome some horrific obstacles.

As a 13-year-old in Decatur, Ga., he came home one day to find his mother killed by a gun shot to the head. He moved in with his father, who just a few months later died of pancreatic cancer. His uncle Kevin Dockett took the boy in and provided him the foundation to eventually succeed.

"The biggest thing for me and my life and my situation is for young people to understand that anything's possible," Dockett said. "I'm living proof. I don't do things for a pat on the back or things like that. I just want people to understand that things are possible. All you've got to do is make the right decisions and keep playing and stay focused."

Over the last three seasons, his 20 sacks are more than fellow defensive tackles Albert Haynesworth (17.5), Kevin Williams (17.5) and Tommie Harris (15.5). Dockett said he feels the new contract pays him what he deserves compared with others at his position.

"I did a lot of research, a lot of thought about it and it's good for me," he said. "I'm very happy."

The news conference was packed with television crews and reporters, a big turnout that could be attributed to the fact that many assumed it had something to do with quarterback Matt Leinart, who reportedly is a candidate to be traded or released.

Whisenhunt was amused.

"I have to admit I was kind of tickled," he said.