José de Espronceda is widely considered by literary experts and historians to be one of the preeminent Romantic poets of the 19th century. He was schooled by another Romantic, Alberto Lista, and his longer narrative work is often compared with luminaries like Byron.
He was rebellious in nature, which informed many of his characters—adventurous, thrill-seeking womanizers like the Casanova-style seducer in El Estudiante de Salamanca or the tortured lethario lamenting the fate of him and his lover in Óscar y Malvina.
He seems to have a fixation with outcasts—pirates, thieves, and "dangerous" sorts that many women find exciting and attractive. Espronceda's characters helped cement Spanish culture as a bastion of Romanticism as we know it today.
In one of his most famous works, Canción del Pirata (aka Pirate's Song), he ruminates on the dream of living outside the bounds of law and civilized society, of making his own rules, and of literally laughing in the face of danger.
We see examples of this in lines like, "Twenty dams we have made in spite of English, and a hundred nations have surrendered their banners at my feet," or, "That I am the king of the sea, and my fury is to fear," or, "I am sentenced to death! I laugh; fate does not abandon me, and to the one who condemns me, I will hang from an entena, perhaps on his own ship." The narrator is the very archetype for the swashbucklers we see on the silver screen in the following century.
Espronceda's passion and rebelliousness and disdain for restraints, both in society and art, is on full display in Canción del Pirata along with a zest for liberty and a desire to live life on his own terms. These ideals live at the heart of the Romantic era.