Zelo, with its theme of solidarity in the face of poverty and hardship, is emblematic of the new trend, and Ricardo would go on to create and perform many other protest-oriented works. When bossa nova founder Joo Gilberto was still mostly unknown and more or less itinerant, Srgio Ricardo housed him in his apartment for several months. According to Ricardo, it was during this stay that Gilberto introduced him to Marxism and other leftist ideas, which heavily influenced the direction Ricardo would take next with his music. (It seems improbable and ironic that Joo Gilberto, who never really jumped on the protest bandwagon himself, can be sourced as a driver of the Brazilian 1960s protest culture, but appearances can often be deceiving.)