David Warren Ellefson (born November 12, 1964) is an American musician, best known for his long tenure as the bassist and backing vocalist for thrash metal band Megadeth across two stints.

Ellefson initially became an accomplished bassist and honed his songwriting skills while leading several of his own bands through the club scene of North America's Midwest region before relocating to Los Angeles.

Ellefson co-founded the hard rock band the Lucid in 2021 alongside vocalist Vinnie Dombroski (Sponge), guitarist Drew Fortier (formerly of Bang Tango), and drummer Mike Heller (Fear Factory, Malignancy, Raven).

In addition to playing bass guitar in Megadeth and the Lucid, Ellefson had various side projects, which include Temple of Brutality, F5, Killing Machine, and Metal Allegiance.

Ellefson is currently a member of the melodic power metal band Avian, which features singer Lance King.

Ellefson, DeGrasso (Mike Portnoy for 2010), Tim "Ripper" Owens and Andreas Kisser formed the band in late 2008.

In February 2010, Ellefson received a text message from Megadeth drummer Shawn Drover, saying "if ever there was a time for you and Dave [Mustaine] to talk, now is it".

Downing of Judas Priest, Dan Donegan of Disturbed, Brian Welch of Korn, Mark Slaughter, Ron Keel, Jason McMaster of Dangerous Toys, Frank Bello of Anthrax, Chris Adler (Lamb of God, ex-Megadeth), Mark Tremonti of Creed and Alter Bridge, Kiko Loureiro and Dirk Verbeuren of Megadeth, actor Kristian Nairn (Game of Thrones), and more, plus a foreword by My Life with Deth co-author, and Bass Player Magazine editor Joel McIver.

[8] He was not included in the documentary Metallica: Some Kind of Monster showing musicians auditioning for the band, however, and after Newsted's departure the position was ultimately filled by Robert Trujillo (former Suicidal Tendencies, Infectious Grooves and Ozzy Osbourne).

In 2019, Ellefson said since he rejoined Megadeth, he is a salaried member as opposed to being an "equal owner" with Mustaine in order to retain their friendship.

[9] On May 24, 2021, Dave Mustaine released a statement on behalf of the band that David Ellefson had once again parted ways with Megadeth, following allegations of sexual misconduct with an underage fan.

[11] On June 17, 2021, Dave Mustaine announced in his weekly Gimme Radio show that he intended to hire a new bassist to rerecord Ellefson's bass tracks for Megadeth's 2022 album The Sick, the Dying... and the Dead!

With Ellefson on bass, the band also consists of drummer Mike Heller (Fear Factory, Malignancy), guitarist Drew Fortier, and vocalist Vinnie Dombroski (Sponge, Spys4Darwin).

[16] The EP includes a guest performance from Insane Clown Posse vocalist Violent J on the title track as well as a cover of Faith No More's "Epic" retitled as "Sweet Toof".

[18] In 2022, Ellefson formed the death metal band Dieth with Guilherme Miranda on guitar and vocals and Michał Łysejko on drums.

The band plays songs from the first three studio albums of Megadeth live (and sometimes Mustaine-penned Metallica tunes, such as "Jump In The Fire").

[23][24] The EP was released October 30 in North America, and December 18 in Europe, and re-released as an LP titled in Your Face (Again) in March 2016 via eOne Distribution.

[36] It was revealed on the Decibel Geek Podcast in an interview with Ellefson and Fortier that an album very loosely tying into Rock Star Hitman recorded with Vinnie Dombroski from Sponge on vocals, Mike Heller from Fear Factory on drums, Drew Fortier on guitar, and Ellefson on bass would be released in 2021 under the name Lucid.

Not only are the parishioners respectful (no bar fights, spilled drinks and foul mouthed hecklers in the crowd like many secular gigs) but it's a musical event my whole family participates in.

[50] On May 24, 2021, Dave Mustaine released a statement stating that, in light of the recent allegations and an already strained relationship, Megadeth had officially parted ways with Ellefson again.

[10] On May 26, 2021, Ellefson released the following statement:[51] Recently, a very private video was illegally posted on the internet and false allegations were made against me.

I wish my bandmates the best with their upcoming tour.After rejoining Megadeth in early 2010, Ellefson started using his old Jackson Custom and Concert bass guitars and Hartke amps again.

Ellefson plays exclusively with a guitar pick, as he is unable to perform in fingerstyle the fast tempos and palm-muting in many Megadeth songs.