Robert Kanigher mused in letters columns in the 1970s and 1980s that Rock probably belonged to "The Big Red One" (First US Infantry Division) given his appearance on battlefields in North Africa, Italy, and Northwest Europe. Rock's backstory was fleshed out in different comics over the years; generally he is considered to have come from Pittsburgh, Pennsylvania, where he worked in a steel mill. Enlisting after the attack on Pearl Harbor, he went to North Africa as a private but promotion came quickly as his superiors were killed, to assistant squad leader, squad leader, and then platoon sergeant. During the main series, his unit is only ever given as "Easy Company", but no regiment or division is named nor is unit insignia ever shown. Rock is shown to have two siblings ("Sgt. Rock #421") Larry, a Marine fighting in the Pacific and Amy, a nun.