Jeffrey John Hanneman (January 31, 1964 – May 2, 2013) was an American musician, best known as a founding member and co-lead guitarist of the thrash metal band Slayer.

A reserved character, Hanneman rarely gave interviews, and preferred to indulge his interest in German war medals and history.

A bout of necrotizing fasciitis in early 2011 left him battling serious health issues; he was replaced on Slayer's tours by guitarists including Gary Holt.

War films were popular on TV at the time, and Hanneman often joined his brothers in constructing and coloring tank and plane models.

[6] Hanneman was introduced to heavy metal music as a child through his older sister Mary, when she was listening to Black Sabbath at her house.

[9] Hanneman, who was heavily influenced by hardcore punk music, got the other members into the genre, leading Slayer into a faster and more aggressive approach.

The band's drummer Dave Lombardo asserted that his hardcore influences pushed him to play faster,[9] contributing to shape his drumming style.

[10] In 1984, Hanneman, Lombardo and Suicidal Tendencies guitarist Rocky George had a brief hardcore punk side project called "Pap Smear" – the band had many tracks and was due to start recording when Hanneman was advised to avoid the side project by Slayer's producer, Rick Rubin, who is quoted as saying "Aaaah, don't do it, man – this is the kind of thing that breaks bands up!

While he conceded that much of the dark subject matter in his songs was "quite ridiculous", his extreme Satanic lyrics were ultimately "an easy way of offending people".

[17] Pat O'Brien (Cannibal Corpse) joined as Slayer's temporary second guitarist when Holt left the tour to play with Exodus.

[18] In 2012, bandmate Tom Araya announced Hanneman's recovery from the infection, though a later update on the band's official website noted that it had "devastated his well-being".

"[15] Holt eventually became Hanneman's permanent replacement in Slayer, remaining with the band for the next six years until they disbanded after finishing their final tour in 2019.

[26] Hanneman's major influences included hard rock and heavy metal bands like Led Zeppelin, Iron Maiden, Judas Priest,[5] Black Sabbath[7] and Aerosmith,[27] and hardcore punk acts such as Wasted Youth, Minor Threat,[28] Dead Kennedys, Black Flag and T.S.O.L.,[5] which heavily influenced his contributions to Slayer's 1996 album Undisputed Attitude.

[30] South of Heaven featured "more technical" guitar riffs, utilizing the aforementioned tremolo picking and down-picked notes, improving musicianship while retaining a melodic sense.

John Consterdine of Terrorizer magazine noted: "without Jeff Hanneman, Slayer certainly would not have created some of the most famous riffs in metal, which undoubtedly changed the entire genre".

[36] Hanneman wrote the music for most of the band's fan favorites, songs such as "Angel of Death", "Raining Blood", "Die by the Sword", "South of Heaven", "War Ensemble", "Postmortem", "Dead Skin Mask" and "Seasons in the Abyss", which have all become staples for live performance at Slayer shows.

[5] Hanneman often composed riffs at his house, using a 24-track and a drum machine and then by gathering opinions from the other band members; King and Lombardo made suggestions of alterations.

Musicians such as Robb Flynn[37] (Machine Head), Dino Cazares[37] (Fear Factory, Divine Heresy), Mille Petrozza[38] (Kreator), Andreas Kisser[39] (Sepultura), Dan Lilker[40] (Anthrax, Nuclear Assault), Eric Hoffman[40] (Amon/Deicide), Trevor Peres[40] (Obituary), Mark Morton[41] (Lamb of God) and Kelly Shaefer[40] (Atheist) cited him as an influence on their playing and songwriting.