He died of liver failure, at the Hemet Valley Memorial Hospital. He was 49.
Although the rhythmic heart and soul of one of the heaviest bands in modern music, Hanneman was known as a soft-spoken, easygoing dude.
See also: Our Jeff Hanneman obituary
To pay tribute, we've reached out to players and peers he performed and spent time with for nearly three decades.
Below, members of Anthrax, Megadeth, Testament and others -- including Slash -- reflect on Hanneman and his contributions, and how he will be remembered.
"For me, Jeff Hanneman was the king of thrash/speed metal guitar. Slayer was the first speed metal band I ever listened to; the riffs & chord changes were genius. And that right hand blew my mind. Never heard anything quite like it."
David Ellefson, Megadeth
"Jeff was a low key public figure, but behind the scenes he was the engine that drove the machine of Slayer's music. His riffs, lyrics and fascinations with dark topics were so extreme that they were taboo even within metal music! But, because he dared to go there, he and the band became legend to fans everywhere. Behind all the bravado of Slayer's image and music, I knew Jeff as a kind and jovial man who always shared a laugh whenever we saw each other on tour together. He always struck me as someone who had his act together off the stage and as a result we would talk our personal and family lives away from music. He was a man of few words but when he spoke his words had impact."
Scott Ian, Anthrax
"There was a real dichotomy knowing Jeff. On one hand he was a really great guy, easy-going, very kick-back and chill, friendly, loved to laugh, and on the other hand he wrote some of the darkest, most brutal lyrics and riffs in the history of metal. If he had only ever written 'Angel Of Death' that alone would be enough to claim the throne of evil, let alone the catalogue of work he created. He was a singular talent and a fun person to be around. I'll miss him."
Charles Benante, Anthrax
"Jeff had a great fucking laugh, I heard it quite a bit throughout the years. The man who wrote such lyrics as "feel the knife pierce you intensely" had a great sense of humor. I will remember him for the music he gave and the intensity he brought to our metal world."
See also: The 20 Greatest Metal Albums in History
Alex Skolnick, Testament
"Like millions of others, I was deeply saddened to hear of the passing of Jeff Hanneman. Personally, I did not know Jeff well, despite our bands having done several tours together. He was someone with his own inside humor and he seemed to view life through the lenses of a wild party in which only those closest to him were invited.
But those he did let in clearly loved him a lot and will miss him dearly. Kerry King may have had the imagery, becoming the "face of Slayer". Tom Araya may have had the voice, so much so that Slayer is one of the few bands that has no background vocals during live shows. Drummer Dave Lombardo provided the musical virtuosity -- his playing forced drummers around the world to lock themselves away and rethink their technique. All four band members created the sound.
But it was Jeff Hanneman who brought in many of the band's most essential riffs. Ask any metal fan to list his or her personal favorite Slayer songs and it's a pretty safe bet that they'll mention one or more of the following sonic assaults, each composed by Hanneman: "Angel of Death," "Raining Blood," "South of Heaven," "War Ensemble," "Dead Skin Mask," "Seasons In The Abyss" and "Die By the Sword." For creating them, we all owe a big debt of gratitude to Jeff Hanneman."