Gibson brought in a Detroit automobile engineer, Roy Deitrich, to dream up a new design for a solid-bodied guitar to compete with Fender, whose twangy ash- and alder-bodied instruments were "the sound" of the early sixties. Starting off with the 1958 Explorer, and then rounding off its sharp edges, broadening the waist and retaining its "upside down" appearance, the Firebird body was born. The head-stock was designed to look like a roosting bird, and heavy-duty banjo-style tuning machines with keys protruding from the rear were fitted in-line, like a left-handed Fender head. Four versions were offered: a basic entry-level I (single pickup, un-bound fingerboard with dot inlays); the user-friendly III (2 pickups, bound fingerboard, flat-handle tremolo system); the deluxe V (2 pickups, crown finger-board inlays, fancy bone-handle leaf-and-lyre tremolo with Tune-O-Matic bridge); and top-of-the-range VII (3 pickups, bound ebony fingerboard with pearl block inlays, deluxe tremolo system, all gold-plated). In addition, two companion basses were added to the range, the Thunderbird II and IV. Like all Gibson solids, they were made from choice British Honduras mahogany, but utilized a construction idea borrowed from Rickenbacker, a two-piece neck and center body section that ran the whole length of the guitar.