Considered the greatest name in Portuguese poetry since the sixteenth-century poet Vaz de Camoes, Fernando Pessoa has often been described as the quintessential modernist, an artist whose work addresses the principal philosophical, psychological, and spiritual questions of the twentieth century. In fact, as Gabriel Josipovici wrote in his Lessons of Modernism, Pessoa is among the few truly representative poets of our time: "When I think of what is most radical in the literature of the past hundred years, of what embodies most clearly the essential spirit of modernism, I think of five grey-suited gentlemen: Constantin Cavafy, Franz Kafka, T.S. Eliot, Fernando Pessoa, Jorge Luis Borges."

Pessoa was born into a cultured Lisbon family. His father, who was a music critic, died when the future poet was five, and a year later his mother married the Portuguese consul to South Africa. Educated in South Africa, Pessoa excelled in English, winning the Queen Victoria essay prize in competition with nine hundred other students. At the age of fifteen he was composing English sonnets in the style of Shakespeare; these poems were later collected and published as Thirty-Five Sonnets (1918). Returning to Portugal in 1905, Pessoa briefly attended the University of Lisbon, eventually securing an office job as a commercial translator, an occupation in which he remained for the rest of his life. He did continue to write poetry, but it was not until 1912 that Pessoa began composing poems in Portuguese. Around that time he became associated with poets of the saudosismo movement, whose works expressed a longing for Portugal's glorious past. By 1915 Pessoa was well known as a modernist poet and critic in Lisbon, gaining renown as one of the founders of Orpheu and Presenca, highly influential literary journals. Most of Pessoa's poetry published during his lifetime appeared in literary journals and remained uncollected; with the exception of his English poems, only one volume of verse, Mensagem (1934), appeared during his life. At the time of his death Pessoa's work was not widely known outside of Portugal; consequently, his international reputation is almost entirely based on posthumously published works.

Two subjects predominate in Pessoa's poetry: the elusive and deceptive nature of personal identity and the individual's limited power to apprehend reality. In order to explore these related themes in the most comprehensive manner, he invented a variety of literary alter egos, each with a different world view. Pessoa termed these persons heteronyms, in contrast to the usual designation of "pseudonym." By providing each heteronym with an imaginary biography, philosophical outlook, and characteristic style, Pessoa attempted to create several distinct literary oeuvres. In essence, Pessoa tried to consider each aspect of his personality as an independent entity. In his poetry, this fragmentation of self is evoked by the frequent use of mask symbolism. The recurrence of masks in Pessoa's poetry has also been related to his family name, which derives from the Latin word persona referring to the mask worn by an actor and, by extension, to the role an actor plays. Acutely aware of the many associations brought forth by his name, the poet occasionally created puns on the word "pessoa," which in Portuguese means both "person" and "nobody."

The first heteronym Pessoa created was Alberto Caeiro, whose philosophical views are those of a pagan materialist and whose poetic style is free verse. When writing as Caeiro, Pessoa repudiated all forms of supernaturalism and celebrated a natural existence in which appearances are accepted at face value. In "Guardador de Rebanhos" ("The Keeper of the Flock"), for example, Caeiro praises the senses as the only legitimate basis for knowledge, proclaiming: "I think with my eyes and with my ears." In a letter written to Adolfo Casais Monteiro in 1935, Pessoa described the birth of this heteronym: "[It] was March 8th 1914—I approached a high chest of drawers, and, taking a sheet of paper, I began to write, standing up, as I always write whenever I can. And I wrote thirty or so poems at a stroke in a kind of ecstatic trance, the nature of which I will not be able to define to you. It was the day of triumph in my life and I shall never succeed in living another like that. I opened with the title 'The Keeper of the Flock' ('O Guardador de Rebanhos'); and what followed was that someone emerged from within me, and whom I christened that very moment Alberto Caeiro. Forgive me for the absurdity of the following sentence: my master emerged from within me."

Like Caeiro, Pessoa's second heteronym, Ricardo Reis, is committed to an exclusively sensual reality, and his neo-classicist "paganism" is derived in large part from his acknowledged master, Caeiro. But, whereas Pessoa assumed the role of a naive pastoral poet when he wrote as Caeiro, Reis is a sophisticated and world-weary fatalist who composes poems in fixed forms rather than free verse. Reis's philosophy of resignation is illustrated in "Quando Lidia, vier o nosso outona" ("When, Lydia, Our Autumn Comes"), an exhortation to "seize the day" in view of the ephemeral nature of human existence. Pessoa adopts another philosophical perspective when he takes on the role of the modernist poet Alvaro de Campos, another heteronym. In the exclamatory free verse Pessoa wrote as Campos, critics have observed two contrary impulses. The first, seen in such poems as "Ode triunfal" ("Triumphal Ode") and "Ode maritima" ("Maritime Ode"), conveys a feverish desire to be everything and everyone, declaring that "in every corner of my soul stands an altar to a different god." The second impulse is toward a state of isolation and a sense of nothingness. In "Tabacaria" ("Tobacco Shop"), for instance, Campos is pictured alone in his room, questioning his own existence: "Just as those accustomed to invoke spirits invoke spirits/I invoke Myself and find nothing." In addition to these three major heteronyms, under which Pessoa wrote much of his poetry in Portuguese, he wrote a variety of works under other heteronyms and "semi-heteronyms," and still others under his own name.

In the 1935 letter to Casais Monteiro, Pessoa described his relation to the heteronyms through which he wrote: "I . . . created a non-existent coterie. I established it all in patterns of reality. I graded the influences, was aware of their friendships, heard within me the discussions and the differing of judgements and in all this it seemed to me that it was I, creator of everything, who had the least to do with it all. It seemed that everything took place independently of me; and it seems that this is still taking place in the very same way. If one day I am able to publish the aesthetic discussion between Ricardo Reis and Alvaro de Campos, you will see how much they differ from each other and how I am nothing in this matter."

Pessoa also composed poetry under his own name, which he considered simply another literary alias, designating it an "orthonym." Many of his best poems were written under this name, including those that reveal his interest in occult studies. As a poet open to occult imagery, Pessoa structured his collection Mensagem, which ostensibly related the legend of King Sebastian's resurrection as Portugal's savior, according to occult paradigms charting an initiate's spiritual progress toward enlightenment. Intrigued by esoteric learning and spiritual traditions, Pessoa nevertheless remained uncommitted to any specific doctrine. In his introduction to Pessoa's Selected Poems, Peter Rickard observed that Pessoa "refuses to choose, to commit himself to any god, for that would mean exchanging the reality for the appearance, the unlimited for the limited, the transcendental for the immanent, the occult for the positive, the soul for the surface."

The majority of the critical work on Pessoa's poetry in English translation has focused on the significance of the heteronyms, and some of this work takes a psychological approach to the poetry. Jonathan Griffin, writing in his introduction to an edition of the Selected Poems of Pessoa, is an example of this approach: "Fernando Pessoa is the extreme example of what may be the essentially modern kind of poet: the objective introvert. None has more consistently tried to find his real self with its multiplicity intact and to keep his poems impersonal." Pessoa himself, in his 1935 letter to Casais Monteiro, signaled this response, when he stated: "the mental origin of my heteronyms lies in my organic and constant propensity toward depersonalisation and simulation," propensities he attributed to "the profound streak of hysteria which is existent within me." Other critics have adopted this approach to Pessoa's work. "Pessoa anticipated in art by sixty years the multiple-personality theory in science," asserted Joanna Courteau in an essay collected in The Man Who Never Was: Essays on Fernando Pessoa. "The heteronyms . . . could be interpreted as Pessoa's representation of man's attempt at listening to and expressing the various voices within." For some, this focus on the slippery nature of individual identity is what makes Pessoa the emblematic poet of the twentieth century.

Though virtually unknown at the time of his death, even in his native Portugal, due to the small amount of work he had published during his lifetime, Pessoa has risen in reputation in the decades following his death. Hispanist Henryk Ziomek, in an essay published in Kentucky Romance Quarterly in 1973, announced that Pessoa's reputation had been resurrected by critics who "[recognize] him as one of the best Portuguese poets in this century." These critics "point to the depth and originality in his work, especially in his aesthetic transposition of psychological drama," Ziomek continued. "Time also made it evident that Pessoa exercised progressive influence on contemporary Portuguese poets." Other critics make even greater claims for the poet, comparing him to Dante, Shakespeare, and other seminal figures in the history of world literature. As Alberto de Lacerda has written: "I shall venture to say that, given the tragic implacable light which Pessoa throws on identity, on responsibility, poetic and otherwise, on shifting the notion of sincerity from the lyrical impulse to intellectual and psychological honesty, he is not the greatest but the most emblematic poet of the Twentieth Century, as Baudelaire was for the Nineteenth Century."