This moped is a surprise in many ways and is the only known example produced under this name. There is a high level of craftsmanship in its construction and finish which was not unheard of at the time. It is possible that it was built by a skilled mechanic for personal use but that is just speculation.
**The name Sotero has its origins in the Greek language and culture, dating back to ancient times. It is derived from the Greek word “soter,” which means “savior” or “deliverer.” This name was initially associated with deities or heroes who were believed to have saved or delivered people from various forms of peril or hardship.
**Source: http://namecensus.com/first-names/sotero-meaning-and-history/
For bespoke builds, the most important component to acquire is an engine. In this case, the engine used is a German marque, the Sachs M32, 98cc (48mm x 54mm), air cooled, two stroke, single with a 2-speed gearbox. These engines were launched in 1932 and, according to the museum, this unit dates from 1936, although the bike is believed to have been finished in 1957. These engines had a long production run, and, by 1945, there had been over 750,000 units built and they were used by manufacturers in Germany, France, Belgium, Scandinavia, Eastern Europe, and South America.
This motorcycle was photographed at the Museo de la Motocicleta Española, 28802 Alcalá de Henares (Madrid) and this is their Data Sheet.
Spanish Motorcycles 