Robert "Bob" Hartman (born December 26, 1949, in Bryan, Ohio) is a Christian artist, guitarist, writer and songwriter. He is the founder of Christian rock band Petra. Hartman was involved with the band from its foundation in 1972 to its end in 2005. He took a break from touring in 1995, but continued to write most of the band's songs, record guitars and produce most of the albums. He officially returned to touring with Petra in 2003 until he decided to retire the band in late 2005.

Bob Hartman learned to play guitar when he was 13 years old, teaching himself from books and watching other people. He has said that one of his major influences was Joe Walsh, a member of The James Gang at the time.

Hartman converted to Christianity when he was a teenager. When he was 21, he joined a Christian band called Rapture with John DeGroff. During this time, he wrote some of the songs of the first Petra album. He also studied at Bowling Green State University, earning a B.A. in Psychology.

When Rapture broke up, DeGroff moved to Fort Wayne, Indiana to attend Christian Training Center (a school based on a church there). Hartman was already jamming with guitarist Greg Hough and they both moved to Indiana to attend the same school. Upon meeting drummer Bill Glover there, they formed Petra. Hartman became the principal (and most of the time, the sole) songwriter of the band, writing the lyrics and music for almost all of their songs.

Piers Lane (born 8 January 1958) is an Australian classical pianist. His performance career has taken him to more than 40 countries. His concerto repertoire exceeds 75 works.

His English father and Australian mother met while auditioning as piano students for the Royal College of Music. Although born in London, he grew up in Brisbane. He graduated with a Medal of Excellence from the Queensland Conservatorium of Music, where his teacher was Nancy Weir, winning the Margaret Nickson Prize in 1978 and the Ruby C Cooling prize in 1977 and 1978. He was later awarded an honorary doctorate by the conservatorium.

He first came to prominence at the inaugural Sydney International Piano Competition in 1977, at which he was named Best Australian Pianist (he was a judge at the 2004 competition). He later studied overseas on a Churchill Fellowship.

Highlights in the past two years have included concerto performances at Avery Fisher Hall, Lincoln Center in New York with the American Symphony Orchestra under Leon Botstein; Beethoven’s Emperor Concerto with The Queensland Orchestra, which received a Limelight Award for Best Orchestral Concert of 2007; concerto appearances with the City of Birmingham Symphony, London Philharmonic, Hallé and Ulster Orchestras; a solo recital in Birmingham’s Symphony Hall for the BBC; a three-recital series called Metamorphoses and an all-Chopin recital at the Wigmore Hall in London; and appearances in many major piano festivals in the United States, the United Kingdom, France, Germany, Italy and Scandinavia. He has also played with all ABC and BBC Orchestras, the Aarhus, City of Birmingham, Bournemouth, Gothenburg and New Zealand Symphony Orchestras, the Hallé, Philharmonia, Kanazawa Ensemble and City of London Sinfonia, the London, Royal Liverpool Philharmonic and Royal Philharmonic Orchestras and the Orchestre National de France among many others. He has been soloist five times at the BBC Proms in London’s Royal Albert Hall.

Gregory Xavier Volz (born January 12, 1950 in Peoria, Illinois) is a Christian singer. He is most noted for being the former lead singer of Christian rock band Petra from 1979 to 1985 and is currently the lead vocalist of the reunited lineup.

Volz showed great skills in singing from a very early age. Being a self-taught musician, when he was 13 years old, he started his own band called The Wombats. As he grew up, he went on to share the stage with the likes of Janis Joplin, Chicago and others. He formed a band called Gidians Bible in Indianapolis. In 1970 he became a born-again Christian. Gidians Bible fell apart and together with drummer David Eden, Volz formed a new band called e Band, which was a part of the Jesus Movement. e's only studio recordings can be found on the rock musical 2LP-album Because I Am released in 1973. Volz married Becky Britton on December 2, 1973, but ended up divorcing in the late 1990s. After e broke up in 1975 Volz moved to Springfield, Missouri, where he worked with legendary guitarist Phil Keaggy. He also performed the lead role in a rock stage musical called Ezekiel.