In October 2010, Seau survived a 100-foot plunge down a seaside cliff in his SUV, hours after he was arrested for investigation of domestic violence at the Oceanside home he shared with his girlfriend. The woman had told authorities that Seau assaulted her during an argument.

There was no evidence of drugs or alcohol involved in the crash and Seau told authorities he fell asleep while driving. He suffered minor injuries.

"I just can't imagine this, because I've never seen Junior in a down frame of mind," Beathard said. "He was always so upbeat and he would keep people up. He practiced the way he played. He made practice fun. He was a coach's dream. He was an amazing guy as well as a player and a person. This is hard to believe."

Seau's ex-wife, Gina, told the Union-Tribune San Diego that he texted her and each of their three children separate messages: "I love you." She later confirmed to The Associated Press that Seau texted the family.

Seau, who played in the NFL for parts of 20 seasons, is the eighth member of San Diego's lone Super Bowl team who has died, all before the age of 45. Lew Bush, Shawn Lee, David Griggs, Rodney Culver, Doug Miller, Curtis Whitley and Chris Mims are the others. Causes of death ranged from heart attacks to a plane crash to a lightning strike.

Gina Seau said her ex-husband sustained concussions during his career.

"Of course he had. He always bounced back and kept on playing," she said in a phone interview. "He's a warrior. That didn't stop him. I don't know what football player hasn't. It's not ballet. It's part of the game."

Gina Seau said she didn't know if the effects of concussions contributed to Seau's death.

"We have no clues whatsoever. We're as stunned and shocked as anyone else. We're horribly saddened. We miss him and we'll always love him," she said.

When Humphries joined the Chargers in a 1992 trade, he said it was obvious Seau was "the person who had the most energy, the most excited, the guy who tried to rally everybody." Humphries said Seau "brought out a lot of youngness" in older players.

He also helped younger players.

"So sad to hear about Jr Seau," tweeted New Orleans Saints quarterback Drew Brees, who was with San Diego from 2001-05. "Junebug. Buddy. The greatest teammate a young guy could ask for. This is a sad day. He will be missed greatly."

Chargers president Dean Spanos called Seau an icon and a friend.

"I can't put into words how I'm feeling right now. I'm shocked and devastated," Spanos said in a statement. "Junior was my friend. We all lost a friend today. Junior was an icon in our community. He transcended the game. He wasn't just a football player; he was so much more. He was loved by everyone in our family, our organization and throughout the NFL.

"This is just such a tragic loss. One of the worst things I could ever imagine. My prayers go out to Junior's family. It's heartbreaking."

Seau called many of those around him "Buddy" and often referred to teammates as "my players."

"As a young linebacker, Junior was my hero growing up and once I had the opportunity to meet him I saw that he was everything I hoped he would be and more," former Dolphin Zach Thomas said in a statement. "Getting the chance to play alongside of Junior Seau, the greatest linebacker to ever play the game, made my dreams come true. I am absolutely devastated to hear this news. Today I lost my hero, my friend, my buddy."

Jason Taylor, who also played with Thomas and Seau on the Dolphins, said he was "devastated."

"It would be easy for me to say he was a great friend and teammate, and a tremendous competitor, but that would be selling Junior short," Taylor said in a statement. "Junior Seau was an individual of great honor and integrity, a leader of men and someone with a deep-rooted passion for giving of himself to make the people, the community and especially the children around him better. This is an immeasurable loss for so many. My heart and prayers go out to Junior's family, Gina and their children. I'm going to miss you buddy."