Although dobro, a resophonic guitar, originated in the US, without its genial developer called Ján Dopjera (John Dopyera as the English version of his name), who came from Slovakia, the Americans would not have been able to call it their own and add it to their cultural heritage. The dobro guitar does not belong only to museums, is not part only of exhibits, but is still being played and actively used by professional musicians of the present day all over the world in various musical genres, from country, blues, jazz, up to pop music. It is important to define its place in the system of musicology, where it forms a part of its organological discipline since dobro is not only a guitar but also involves a sophisticated technological system. In this paper, I deal with the division of string instruments which make use of the dobro system. I analyse the materials which are most frequently used for their manufacturing. I devote attention to the strings used by the musicians, and to how they switched from thin strings to thicker ones. In the music of the most well-known performers and bands, the “dobro” system most often made use of guitars with a wooden body. Later, they switched from the resonating system to electromagnetic sensors. I discuss not only the development of the instrument but also the life of its inventors, the Dopyera brothers, sons of a miller from Dolná Krupá near Trnava in western Slovakia. The Dopyeras moved to Los Angeles, USA, for work, in 1908. Unfortunately, the agitated and conflictful relationship of the investor, George Beauchamp, with John Dopyera affected the development of the “dobro” system as well. When the original American dobro guitars made their way to Slovakia in the 1990s, it meant a new development in the cultural relationship of the Americans and the Slovaks.