John DeGroff
DeGroff was one of the original members of Christian rock band Petra in 1972 , along with Greg Hough , Bill Glover and Bob Hartman . 
<triplet> Petra <subj> Christian rock <obj> genre <subj> 1972 <obj> inception <triplet> Bill Glover <subj> Christian rock <obj> genre <subj> 1972 <obj> work period (start) <triplet> Bob Hartman <subj> 1972 <obj> work period (start)