Sadiki Fuller, who was the first Thunder and wore the costume from 1997 to 2002 passed away at the age of 44.
There is no word on his cause of death.
The Warriors had to give up the mascot when the Oklahoma City Thunder took the team nickname in 2008.
Former Warrior and ABC7 Sports contributor Adonal Foyle tweeted his condolences to Fuller.
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In 1997, I was a rookie with the @Warriors. That same year, the team introduced #DubNation to our mascot Thunder! The man behind the mask was a lovable soul who always wanted to make people smile, as a mascot and as a standup comedian! Rest in paradise @sadikifuller! We’ll miss U pic.twitter.com/yQIqhTlDkz— Adonal Foyle (@afoyle3131) May 17, 2018