Derek Jupiter (portrayed by Steve Valentine) is Iron Weasel's cocky, but fairly charming lead singer.

Derek Jupiter was born in London, England on 1970. He moved to the United States at the age of six. When Derek saw his dog's buttocks in 1984 it inspired the name of his hard rock band named "My Dog's Butt" while going to high school with his childhood friends Andrew "Burger" Pitt and Ashley "Ash" Tyler. The band started recording demos at Derek's room, which later became his makeshift studio. The band sent the demos to record labels, but none replied. The band changed its name to "Derek Jupiter and The Other Guys", a year later. Two months later, the two members asked Jupiter to change the band's name. He said no, three attempts later he agreed. Derek saw a weasel, which was crushed by iron which later inspired the band's name and "Iron Weasel" was born. In the mid-1990's, Derek dated his roadie Ernesto's girlfriend, Julie. When Iron Weasel split up in 2001, he had a solo career with the album "Derek". His album flopped and later lived with his ex-band mates in The Band Van a year later. Seven years later the band reunited, along with their new lead guitarist Tripp Campbell. Derek is now the lead singer of Iron Weasel.