F5 is a 2002 band unit founded by former MEGADETH bassist David Ellefson. As a central lynchpin and staunch ally of Dave Mustaine's, the bassist had appeared on every single MEGADETH album, a feat unrivalled by any other band member. Joined by guitarists Steve Conley and John Davis, drummer David Small and erstwhile G.I.V.E. and SICK SPEED singer and Minneapolis native Dale Steele, F5 worked on recordings with producer Ryan Greene for a projected album release.

F5 would shop a five song demo in July, these sessions, cut with producer Ryan Greene, including a cover rendition of EDIE BRICKELL AND THE NEW BOHEMIANS 'What I Am'. The band undertook a 4th October showcase gig at The Roxy in West Hollywood, California alongside METAL SKOOL, SOUND OF STRUGGLE and FACE THE DAY.

It would be learned in early 2005 that Ellefson had convened a brand new band unit entitled ENEMY OF GOD. This alliance found the bassist partnered with the SLAYER, TESTAMENT and PUSHED credited Jon Dette on drums, PUSHED, STREAM, BELLADONNA and KILLING MACHINE French guitarist Peter Scheithauer and Todd Barnes of 13-A on vocals. By April, with Dette being replaced by W.A.S.P.'s Stet Howland, this project had morphed into TEMPLE OF BRUTALITY. Another side activity for the bassist saw him joined forces with WHITEHEART member Billy Smiley to form the Christian worship band SYMPHONY IN RED.

F5 signed to the Japanese label JVC Victor for Asian license for the 2005 album 'A Drug For All Seasons', shortly afterward securing a European deal with Holland's Mascot Records. In August Ellefson substituted for a brace of SOULFLY gigs in Tempe, Arizona and Long Beach, California, regular bassist Bobby Burns forced to miss the shows due to a "family emergency".

Word arrived in January 2006 that Ellefson, alongside former MEGADETH drummer Jimmy DeGrasso, was featured in RONNIE MONTROSE's live band and on his album 'Ronnie Montrose and Friends: 10x10'. The bassist also guested on the album 'Modes Of Alienation' by Boston based, instrumental Progressive Metal project THE ALIEN BLAKK. F5 undertook US shows throughout June, these seguing into a brief tour on the East Coast alongside guitarist MARC RIZZO and the ALEX SKOLNICK TRIO in July.

In September Ellefson temped for SOULFLY's North American dates after regular bassist Bobby Burns suffered a mild stroke.

It was announced in December 2008 that Ellefson, together with guitarist Andreas Kisser, of SEPULTURA, vocalist Tim "Ripper" Owens, of JUDAS PRIEST, BEYOND FEAR, YNGWIE MALMSTEEN and ICED EARTH, and drummer Jimmy DeGrasso, from ALICE COOPER and MEGADETH, would be touring Chile between 22nd and 27th January 2009 for five shows, in Santiagho, Valparaiso, Concepcion, Puerto Montt and Antofagasta, under the collective name HAIL!