Rockers (also known as leather boys and ton-up boys) are members or followers of a rock and roll and biker subculture that originated in the United Kingdom during the late 1950s and remained popular in the 1960s, especially among youths. Rockers who rode bikes were widely known as ton-up boys for achieving a speed of 100 mph (miles per hour). By 1965, the term greaser had also been introduced to Great Britain and, since then, the terms greaser and rocker have become synonymous within the British Isles, although used differently in North America and elsewhere. Rockers were also derisively known as coffee bar cowboys. Their Japanese counterpart was called the kaminari-zoku (thunder tribe/clan/group, or thunderers).