Mulders introduced the flamenco guitar in the Netherlands, performed in the San Francisco Bay Area, and recorded Mexican indigenous music in the 1950s.
In 1936 Mulders and Maarten travelled to Italy as correspondent of the Dutch communist newspaper De Tribune.
The Spanish Coup of July 1936 prompted Mulders to join a Republican militia to help build barricades around the Montjuic Castle.
Because of his knowledge of mechanical engineering and his military background, Mulders joined the international group of the Durruti Column that marched to Zaragoza.
Mulders joined the resistance group CS-6 (Sabotage Committee number 6) together with other Dutch veterans of the Spanish Civil War such as Jef Last, whose book Elfstedentocht (Eleven cities tour) mentions Mulders participation in the skating event in 1940.
He provided the music for the Dutch version of the theater play Guardate del Agua Mansa by Pedro Calderón de la Barca, a play that was performed over 50 times in different theatres in the Netherlands around 1946, earning him the fame of having introduced classical Spanish guitar to the Dutch audience.
Mulders became a member of the Chicago Classic Guitar Society but soon took the opportunity to accompany a flamenco dancer to New York.
Soon he moved to California where he joined the Bay Area Classic Guitar Society and found a job in restaurant Goya in San Francisco as cook and guitarist.
Mulders, with the stage name Guido Daunic, was part of the Baroque Players, a band founded by Paul Ashford.