After 12 years and two Super Bowl wins, one of the greatest players to ever put on a Pittsburgh Steelers uniform has decided to retire.

Troy Polamalu told the Uniontown Herald-Standard on Thursday night that he's decided to hang up his cleats after playing 158 regular season games in a Steelers uniform. 

For Polamalu, the decision to retire wasn't easy, but it came down to one thing: His family. 

Here's five things to know what Polamalu's retirement. 

1. Polamalu is retiring because of his family.

After taking four months to think about it, Polamalu's decision to retire came when he started thinking about his family.

"It's all about family," Polamalu said on Thursday. "I live here in Pittsburgh now, and since the end of the season I've had a chance to enjoy my family on a level I never had before. It was awesome."

What this means is that Polamalu didn't retire to pitch Head and Shoulders full-time, so you can throw that theory out the window. 

Polamalu said that if he was younger, he would've looked to continue his career somewhere else, but at age 33, that's not something he was interested in.

"If I'm in my fourth-year, fifth-year, even if I'm in my 10th-year, I'm playing in Alaska," Polamalu said. "But when I started this process and started to debate whether I should come back or should I play, that was kind of the sign for me to say 'Whoa, if you're just even debating it maybe you shouldn't play anymore,' because what I do know about this game is it takes a lot -- a lot -- of commitment just to be an average player."

2. Polamalu definitely wasn't an average player.

If you watched any Steelers game over the past 12 seasons, you saw a player in Polamalu who basically reinvented the safety position.

From Day 1, the Steelers knew the former USC football player was special, which is why Pittsburgh traded up to get him in the 2003 NFL Draft.  

Going into the draft, the Steelers held the 27th overall pick, but they ended up trading into the 16th spot to grab Polamalu. To move to No. 16, the Steelers had to give up their 27th overall pick, along with a third-round and a sixth-round pick.

As far as draft trades go, Pittsburgh hit a home run.

During his 12 seasons with the team, Polamalu went to eight Pro Bowls, was named first-team All-Pro four times and even won a defensive player of the year award in 2010. Over 158 regular season games with the Steelers, Polamalu recorded 771 tackles, 32 interceptions and 12 sacks.

Polamalu also had no regard for snap counts.  

And let's not forget that Polamalu also won two Super Bowls in Pittsburgh.

One of Polamalu's best years came in 2008, the year the Steelers won Super Bowl XLIII over Arizona. During the 2008 season, the safety picked off seven passes, which was the second most in the NFL that season. 

The 2008 season also included a game-clinching interception in the AFC title game against Baltimore. 

Despite all the  accolades, Polamalu said that preserving his legacy had nothing to do with his decision to retire.

"I had talked to a lot of people about what I should do with my situation, and what they kept saying back to me, and which was not a sufficient reason, was 'Troy, you played 12 years in the NFL, you won Super Bowls, won individual awards. There's nothing left to prove. You have a legacy,'" Polamalu said. "And I just kept saying, 'First of all, I don't care about a legacy. Second of all, I play the game because I enjoy it.' That's the reason to keep playing."

Fittingly, Polamalu's final four quarters in a Steelers uniform came in a game where he led the team in tackles. In Pittsburgh's 30-17 playoff loss to Baltimore, Polamalu tallied a team-leading eight tackles. 

3. The Steelers will get some slight salary cap relief.

Even when you lose a player like Polamalu, the show must go on and in the Steelers' case, the show will go on with some extra money in the bank. Between his base salary ($6 million) and pro-rated signing bonus ($2.25 million), Polamalu was set to count $8.25 million against the Steelers salary cap this season. 

With Polamalu retiring though, the Steelers will pick up $3.75 million in cap space. The team will take a $4.5 million cap hit in 2015 to pay the rest of Polamalu's signing bonus, however, that's $3.75 million less than the $8.25 million Polamalu would have counted for if he had played this year. After the $4.5 million cap hit, Polamalu will be off the books for good. 

4. The guy who's taking over.

Trying to fill someone's shoes is never easy, trying to fill a future Hall-of-Famer's shoes is almost impossible, but that's what Shamarko Thomas is going to have to do. 

The fourth-round pick out of Syracuse has received ample playing time since being taken by the Steelers in the 2013 NFL Draft. Thomas has played in a total of 25 games over two seasons in Pittsburgh.

However, Thomas has only started two games, which is kind of surprising, given the youth movement the Steelers defense went through. When Polamalu missed the first week of OTAs last season, Will Allen was taking the first team reps, not Thomas. 

Thomas hasn't developed as quickly as the Steelers would like, but he's going to have figure out things soon because he's the next in line now that Polamalu is done.

5. Polamalu had the NFL's respect. 

It's not often that a player is respected by almost everyone else in the NFL, but Polamalu was. After his retirement was announced on Thursday, dozens of NFL players took to Twitter to show their respects. 

Here's a sample of some of those tweets, starting with former Ravens receiver Torrey Smith. 

When he says "crazy things" I think Smith's talking about plays like this. 

Here's a few other tweets, starting with another division rival, Bengals corner Dre Kirkpatrick. 

Troy Polamalu is hanging up his cleats after 12 seasons. (CBS Sports)
Troy Polamalu is hanging up his cleats after 12 seasons. (CBS Sports)