Slayer spokeswoman Heidi Robinson-Fitzgerald says Hanneman died Thursday morning of liver failure at a Los Angeles hospital with his wife, Kathy, by his side.
The guitarist had recently begun writing songs with the band in anticipation of recording a new album later this year. He had been slowly recovering from what was believed to be a spider bite that nearly cost him his arm after he failed to seek immediate treatment.
Robinson-Fitzgerald says it's believed the bite contributed to the failure of his liver, but it is unclear whether an autopsy will be scheduled. No funeral arrangements have been made.
Hanneman co-founded the thrash metal pioneers in Huntington Beach, Calif., in 1982.
