Since the end of the 19 th Century songs composed by our first troubadours began to appear.   They used, developed and even created some musical forms or genres within the general song framework.   One of them was the bolero .   With the New Trova this term came out once more, though now with its own characteristics to designate a music always linked to texts and eminently conceived to be sang and through its singing, express feelings and even criteria and concepts concerning life in general and love in particular.
The song entitled "Tristezas" by Pepe Sánchez was the first Cuban bolero registered by history which had nothing to do with the so-called "Spanish bolero " present in Cuba since the 18 th Century together with other manifestations of similar origin as the fandangos and the seguidillas among others. It is not even a modification of the former.
The first boleros adopted the song form, or structure, with two musical parts or periods, almost always separated by an instrumental part and incorporating to the guitar accompaniment -and, occasionally to the melody- a rhythmic element which is characteristic in our music:   the Cuban cinquillo , also adopted by the danzón and being one of its features, in the beating of the pailas.
The most important composers of the Traditional Trova composed a great number of pieces using this rhythm.   During this stage, including the first decades of the 20 th Century, this genre had its own physiognomy, mainly because of the cinquillo , thus emerging a rhythm that easily merged both the Hispanic and African elements.   We can certainly speak of a traditional or troubadour-like bolero different from the one internationally disseminated and acknowledged some years later.  
During the boom of son and the apogee of danzón , this traditional bolero was partially relegated for it was not eminently for dancing and was not assimilated by the new sonero septets and sextets nor by the typical orchestras or charangas. Nevertheless, we must clarify the fact that during those years, there was still a development of the work of those Cuban troubadours who resorted to their guitar and voices to interpret some of the most beautiful songs in our history, many of them boleros .
At that time, when dancing manifestations prevailed, some composers, not guitar players but pianists, began composing boleros that gradually managed to be different from the previous ones.   The piano, with more expressive possibilities than the guitar, while maintaining the cinquillo as a rhythmic figure in the left hand, allowed the introduction of melodic turns of another kind that finally prevailed over the rigid rhythm of the cinquillo until it finally disappeared.   Likewise, the musicalization of verses also contributed with its disappearance, since it was better to have more freedom without any strong linkage to a rhythmic base.   'Aquellos ojos verdes' is the song that summarizes this process, with music by Nilo Menéndez and text by Adolfo Utrera.  
The paternity -o better to say the nationality- of this bolero has been questioned.   More specifically in Mexico it has been and is still a widely disseminated and enjoyed rhythm and it is said that this country is the promoter of this musical manifestation.   What is unquestionable is that some Mexican composers, like Agustín Lara or María Grever, have contributed a lot with this genre and with its wide international acceptance.   Undoubtedly, their work has influenced Cuban composers who came afterwards.
But obviously the boleros   of our Cuban composers have also influenced considerably the work of Mexican authors and authors from other countries.
We cannot speak of boleros without mentioning their content, evidently loving and intimate verses.   The most loving feelings or disappointments are declared or expressed in a straight and simple language whose texts are sometimes repetitive or extremely simplistic.   The bolero , after becoming a dancing piece, was performed by orchestras of every kind and was an absolute success since it allows the couple to take a breath, dancing more slowly, between two active pieces.
It is impossible to mention some of the most important bolero authors without any omission.   However, the works of René Touzet, Juan Bruno Tarraza, Orlando de la Rosa, Felo Bergaza, Pedro Junco, Luis Marquetti, Isolina Carrillo and Juan Arrondo, are among others unfairly omitted for the sake of   reducing this interminable list.   We must never forget musicians like Adolfo Guzmán, Ernesto Lecuona, Gonzalo Roig or Jorge Anckerman, who composed songs closer to the lyric genre, as well as beautiful boleros or songs that were finally performed as boleros.
Another moment of great importance for this musical genre was the emergence of the feeling -or filin in Cuban language.   Equally intimate, the filin was a movement that taking the song as starting point influenced in almost all the Cuban popular music.   Its promoters returned to the guitar to compose under the influence of the blues and the jazz though rooted too in the trova tradition.   The filin movement, together with its creators, grouped some of the best and more updated arrangers and musicians of that time who joined the troubadours in their informal performances.   Many of the filin songs were interpreted as boleros with excellent orchestral arrangements including vanguard concepts and harmonization.
Together with José Antonio Méndez and César Portillo de la Luz, the most renowned, we should also mention Martha Valdés, Ángel Díaz, Ñico Rojas, Rosendo Ruiz Quevedo, Tania Castellanos and 'Niño Rivera', among the most important creators of this movement.
The most outstanding interpreters of the Cuban popular music included the bolero in their repertoires.   The greatest interpreters of this musical genre included Benny Moré, Panchito Riset, Ñico Membiela, Orlando Vallejo, Olga Guillot, Fernando Álvarez, Gina León, Tito Gómez, Roberto Faz, Pacho Alonso, Roberto Sánchez, Omara Portuondo, Elena Burke and many others.
The bolero had -and still has- a sort of fusion with other Cuban rhythms.   The bolero-son , the bolero-mambo , the bolero-chá are some examples of the link between the bolero and these genres.   Initially, a theme was taken, originally conceived as a bolero and then rhythmic elements from other genres were added to it.   But works previously thought, previously conceived were originally composed from the fusion among musical genres.