Junior Seau’s apparent suicide in Oceanside, California stunned an entire city and saddened former teammates who recalled the former NFL star’s ferocious tackles and habit of calling everybody around him ‘’Buddy.’’

It also left everyone wondering what led to Seau’s death Wednesday morning in what police said appeared to be a suicide. He was 43.

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.

‘’I’m sorry to say, Superman is dead,’’ said Shawn Mitchell, a chaplain for the San Diego Chargers. ‘’All of us can appear to be super, but all of us need to reach out and find support when we’re hurting.’’

Police Chief Frank McCoy said Seau’s girlfriend reported finding him unconscious with a gunshot wound to the chest and lifesaving efforts were unsuccessful. A gun was found near him, McCoy said. Police said no suicide note was found and they didn’t immediately know who the gun was registered to.

Neither Mitchell nor Seau’s ex-wife knew what might have led to the former first-pumping, emotional leader of his hometown San Diego Chargers to kill himself.

‘‘We have no clues whatsoever,’’ Gina Seau said. ‘’We’re as stunned and shocked as anyone else. We’re horribly saddened. We miss him and we’ll always love him.’’

Seau helped carry the Chargers to their only Super Bowl, following the 1994 season. A ferocious tackler, he’d leap up, pump a fist and kick out a leg after dropping a ball carrier or quarterback.

‘’It’s a sad thing. It’s hard to understand,’’ said Bobby Beathard, who as Chargers general manager took Seau out of Southern California with the fifth pick overall in the 1990 draft. ‘’He was really just a great guy. If you drew up a player you’d love to have the opportunity to draft and have on the team and as a teammate, Junior and Rodney (Harrison), they’d be the kind of guys you’d like to have.’’

Seau’s death follows the suicide last year of former Chicago Bears player Dave Duerson, who also shot himself in the chest.

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 sustained 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 told the San Diego Union-Tribune that he texted her and each of their three children separate messages: ‘’I love you.’’

The family of former NFL star Junior Seau will donate his brain for research into repetitive head injuries. San Diego Chargers chaplain Shawn Mitchell said the family made the decision Thursday.