Setra is a brand owned by EvoBus and is a firm that is a subsidiary of Daimler-Benz.

It's origins began in 1883 when Karl Kaessbohrer started the firm and over the years continued making heavy-duty buses, trailers, transporters, etc. Over the years they developed few brands such as Setra and PistenBully (snow moving vehicles) until the mid-nineties when the firm started facing financial problems before the Daimler-Benz Group took it over.

The name Setra is derived from the German word ‘selbsttragend’ which means self-supporting. In the 1940s and 50s when all the buses were basically a body that was separately mounted over the chassis of a truck, the Setra S215HD was a bus that had a self-supporting structure. This model was the third generation bus of the S series and rolled out in 1976. 

Figure 15 in S215 HD indicates 15 seat rows and HD indicates Hochdecker (high deck, in German)

This model was so famous that it also featured in the GTA San Andreas video game.