The Tenor Banjo
Banjos originally were of the 5-string type (actually 3 strings and a drone played flailing style, made of gourd, skin wood and gut - see Beginnings). The Tenor Banjo did not emerge until some time after the 5-string banjo had been introduced to America and came into being a process of evolution.
The banjo, by the end of the 19th century had acquired frets and could be strung with steel strings. It wasn't long before some players started removing the drone string and re-tuning the 4 long strings in different ways.
When these long banjos were made in their own right, with just 4 strings, they became known as Plectrum Banjos and were generally of around 22 to 26 frets to the body. The tuning is usually CGBD but Chicago Tuning (DGBE) is also very popular as it is the same as a guitar. The long length with tuning in fifths made melody playing a challenge, and so the Tenor Banjo arose with a shorter neck (17 or 19 frets), 4 strings and tuned as a tenor - CGDA as the Mandola and Viola. The shorter scale-length banjo (17 fret) is often re-tuned to GDAE and is sometimes known as the Irish Banjo.
Reported variously as originating with the Tango craze (around 1910) or the Jazz craze, the golden era of the Tenor Banjo was definitely in the 1920s and 1930s. After the war it was to be eclipsed by the guitar.