Jeff "Mantas" Dunn (born 22 April 1961) is a British guitarist best known as one of the founder members of seminal thrash/speed metal band Venom, with which he played as a guitarist from 1979 to 1985 and 1989 to 2002.
In 1986 he left Venom to form the band Mantas which so far has recorded two full-length albums: Winds of Change in 1988, and Zero Tolerance in 2004.
In 1992 he played guitars for Warfare, a NWOBHM band from the United Kingdom.
In 2006, Mantas toured with German hardcore techno act Scooter in Germany as an additional member on guitar.As of 2007, Dunn was working with the band Dryll.In 2009, he guested on German metalcore band Last One Dying's debut album The Hour of Lead and released the Dryll EP Digital Surgery which was available at live shows only.
In 2010, Jeff Dunn and former Venom members, Antony "Antton" Lant (drums; brother of Venom frontman Conrad "Cronos" Lant) and Tony "The Demolition Man" Dolan (bass, vocals) are back with their new band, initially called Primevil but now Mpire of Evil.
Dunn played guitar on the track Hold On by Scott Michael Cavagan.
In May 2018, Dunn underwent emergency heart surgery (double bypass) in Lisbon following a life threatening incident.