In 1928, at the Abel Pereira da Fonseca wine house, Fanqueiros Street, Lisbon.
The literary concept of heteronym, invented by Portuguese writer and poet Fernando Pessoa, refers to one or more imaginary character(s) created by a writer to write in different styles. Heteronyms differ from noms de plume (or pseudonyms, from the Greek "False Name") in that the latter are just false names, while the former are characters having their own supposed physiques, biographies and writing styles.
Pessoa's heteronyms 
In Pessoa's case, there are at least 70 heteronyms (according to the latest count by Pessoa's editor Teresa Rita Lopes); some of them are relatives or know each other; they criticise and translate each other's works. Pessoa's three chief heteronyms are Alberto Caeiro, Ricardo Reis and Álvaro de Campos; the latter two consider the former their master. There are also two whom Pessoa called semi-heteronyms, Bernardo Soares and the Baron of Teive, who are semi-autobiographical characters who write in prose, "a mere mutilation" of the Pessoa personality. There is, lastly, an orthonym, Fernando Pessoa, the namesake of the author, who also considers Caeiro his master.
The heteronyms dialogue with each other and even with Pessoa in what he calls "the theatre of being" or "drama in people". They sometimes intervened in Pessoa's social life: during Pessoa's only attested romance, a jealous Campos wrote letters to the girl, who enjoyed the game and wrote back.
Pessoa, also an amateur astrologue, created in 1915 the heteronym Raphael Baldaya, a long bearded astrologue. He elaborated horoscopes of his main heteronyms in order to determine their personalities.
Fernando Pessoa on the heteronyms
How do I write in the name of these three? Caeiro, through sheer and unexpected inspiration, without knowing or even suspecting that I’m going to write in his name. Ricardo Reis, after an abstract meditation, which suddenly takes concrete shape in an ode. Campos, when I feel a sudden impulse to write and don’t know what. (My semi-heteronym Bernardo Soares, who in many ways resembles Álvaro de Campos, always appears when I'm sleepy or drowsy, so that my qualities of inhibition and rational thought are suspended; his prose is an endless reverie. He’s a semi-heteronym because his personality, although not my own, doesn’t differ from my own but is a mere mutilation of it. He’s me without my rationalism and emotions. His prose is the same as mine, except for certain formal restraint that reason imposes on my own writing, and his Portuguese is exactly the same – whereas Caeiro writes bad Portuguese, Campos writes it reasonably well but with mistakes such as "me myself" instead of "I myself", etc.., and Reis writes better than I, but with a purism I find excessive...)
- Fernando Pessoa, Letter to Adolfo Casais Monteiro, 13.01.1935, in The Book of Disquiet, Penguin Classics, 2002, p. 474.
George Steiner on the heteronyms
Pseudonymous writing is not rare in literature or philosophy (Kierkegaard provides a celebrated instance). 'Heteronyms', as Pessoa called and defined them, are something different and exceedingly strange. For each of his 'voices', Pessoa conceived a highly distinctive poetic idiom and technique, a complex biography, a context of literary influence and polemics and, most arrestingly of all, subtle interrelations and reciprocities of awareness. Octavio Paz defines Caeiro as 'everything that Pessoa is not and more'. He is a man magnificently at home in nature, a virtuoso of pre-Christian innocence, almost a Portuguese teacher of Zen. Reis is a stoic Horatian, a pagan believer in fate, a player with classical myths less original than Caeiro, but more representative of modern symbolism. De Campos emerges as a Whitmanesque futurist, a dreamer in drunkenness, the Dionysian singer of what is oceanic and windswept in Lisbon. None of this triad resembles the metaphysical solitude, the sense of being an occultist medium which characterise Pessoa's 'own' intimate verse.
- George Steiner, "A man of many parts", in The Observer, Sunday, 3 June 2001.
Richard Zenith on the heteronyms
Álvaro de Campos, the poet-persona who grew old with Pessoa and held a privileged place in his inventor’s hearts. Soares, the assistant bookkeeper and Campos, the naval engineer never met in the pen-and-paper drama of Pessoa’s heteronyms, who were frequently pitted against one other, but the two writer-characters were spiritual brothers, even if their wordly occupations were at odds. Campos wrote prose, as well as poetry, and much of it reads at it came, so to speak, from the hand of Soares. Pessoa was often unsure who was writing when he wrote, and it’s curious that the very first item among the more than 25,000 pieces that make up his archives in the National Library of Lisbon bears the heading A. de C. (?) or B. de D. (or something else).
- Richard Zenith, introduction to The Book of Disquiet, Penguin Classics, 2002, p. XI.
Alberto Caeiro 
According to a letter by Fernando Pessoa, he collected the name of this important heteronym from a pharmacy in Lisbon called A. Caeiro. Pessoa created this heteronym as the "Master" of his "brothers", including Pessoa itself. Caeiro was a humble man of poor education, but a great poet "naif". However, his poetry is full of philosophy. He wrote "Poemas Inconjuntos" (Disconnected Poems) and "O Guardador de Rebanhos" (The Keeper of Sheep), published by Fernando Pessoa in his "Art Journal" Athena in 1924-25.
Ricardo Reis 
This heteronym was created by Pessoa as a Portuguese doctor born in Oporto, in September 19, 1887. Reis supposedly studied at a boarding school run by jesuits in which he received a classical education. He was an amateur latinist and poet; politically a monarchist, he exiled in Brazil after the defeat of a monarchical rebellion against the Portuguese Republic in 1919. Ricardo Reis reveals his Epicureanism and Stoicism in the «Odes by Ricardo Reis», published by Pessoa in 1924, in his literary journal Athena.
Since Pessoa didn't determine the death of Reis, one can assume that he survived his author who died in 1935. In The Year of the Death of Ricardo Reis (1984), Portuguese nobel prize José Saramago rebuilds, in his own personal outlook, the literary world of this heteronym after 1935, creating a dialog between Ricardo Reis and the ghost of his author.
Álvaro de Campos 
This heteronym was created by Fernando Pessoa as an alter ego who inherited his role from Alexander Search and this one from Charles Robert Anon. The latter was created when Pessoa lived in Durban, while Search was created in 1906, when Pessoa was a student at Lisbon's University, in search of his Portuguese cultural identity, after his return from Durban. Anon was supposedly English, while Search, although English, was born in Lisbon. After the Portuguese republican revolution, in 1910, and consequent patriotic atmosphere, Pessoa dropped his English heteronyms and Álvaro de Campos was created as a Portuguese alter ego. Álvaro de Campos, born in 1890, was supposedly a Portuguese naval engineer graduated in Glasgow. He sailed to the Orient, living experiences that he describes in his poem «Opiarium». He also wrote «Lisbon Revisited (1923)» and «Lisbon Revisited (1926)», while unemployed in Portugal. Thought his master works are «Tobacco Shop» and the «Odes»: «Ode Triumphal» and «Ode Maritime», published in the literary journal Orpheu, in 1915, and other unfinished. Campos was a decadent poet, but he embraced futurism; his poetry was strongly influenced by Walt Whitman and Marinetti.
List of Pessoa's heteronyms 
|1||Fernando António Nogueira Pessoa||himself||Commercial correspondent in Lisbon|
|2||Fernando Pessoa||orthonym||Poet and prose writer|
|3||Fernando Pessoa||autonym||Poet and prose writer|
|4||Fernando Pessoa||heteronym||Poet, a pupil of Alberto Caeiro|
|5||Alberto Caeiro||heteronym||Poet, author of 'O guardador de Rebanhos','O Pastor Amoroso' and 'Poemas inconjuntos', master of Fernando Pessoa heteronyms, Álvaro de Campos, Ricardo Reis, António Mora and Coelho Pacheco|
|6||Ricardo Reis||heteronym||Poet and prose writer, author of 'Odes' and texts on the work of Alberto Caeiro. Biographical note: (Oporto, 1887–1936). He graduated in medicine and is an unconditional admirer of the Greek civilisation above all others, and considers himself to be an expatriate from Greece. Being a royalist he chooses to emigrate to Brazil in 1919 (Portuguese monarchy had been overthrown in 1910). In his neoclassical odes he ponders on the briefness of life, the inevitability of death and the helplessness of the human condition. This “sad epicure” tries to find some contentment through the acceptance of fate and self-discipline lives by Horatio’s a motto: carpe diem (seize the day).|
|7||Frederico Reis||heteronym/para-heteronym||Essayist, brother of Ricardo Reis, upon whom he writes|
|8||Álvaro de Campos||heteronym||Poet and prose writer, a pupil of Alberto Caeiro. Biographical note: Álvaro de Campos. (Tavira, Algarve, 1890 - ?). He studies naval engineering in Scotland. He feels a foreigner wherever he is. Suffocated by a tedious and monotonous existence, failing to see the meaning of life, he looks for new sensations and travels to the Far East. When he comes back he is a renewed man. He embraces the futuristic movement and worships industrialisation and scientific and technological progress, with its hectic relentless rhythm and continuous change. There is an ecstasy of the senses, his relationship with machines and charcoal and steel is almost erotic. But in the background of this modern world lurk the shadows of the assembly line, the pollution, the emptiness of material things. The darkness of what is to come —eventually Campos tires. In his third phase, profoundly disenchanted with the present, he evokes the long-gone days of his perfectly happy childhood.|
|9||António Mora||heteronym||Philosopher and sociologist, theorist of Neopaganism, a pupil of Alberto Caeiro|
|10||Claude Pasteur||heteronym/semi-heteronym||French, translator of "CADERNOS DE RECONSTRUÇÃO PAGÃ" conducted by Antonio Mora|
|11||Bernardo Soares||heteronym/semi-heteronym||Poet and prose writer, author of the 'Book of Disquiet'|
|12||Vicente Guedes||heteronym/semi-heteronym||Translator, poet, and director of Ibis Press, author of a paper|
|13||Gervásio Guedes||heteronym/para-heteronym||Author of the text 'A Coroação de Jorge Quinto'|
|14||Alexander Search||heteronym||Poet and short story writer|
|15||Charles James Search||heteronym/para-heteronym||Translator and essayist, brother of Alexander Search|
|16||Jean-Méluret of Seoul||heteronym/proto-heteronym||French Poet and Essayist|
|17||Rafael Baldaya||heteronym||Astrologer and author of 'Tratado da Negação' and 'Princípios de Metaphysica Esotérica'|
|18||Barão de Teivo||heteronym||Prose writer, author of "Educação do Stoica" and "Daphnis e Chloe"|
|19||Charles Robert Anon||heteronym/semi-heteronym||Poet, philosopher and story writer|
|20||A. A. Crosse||pseudonym/proto-heteronym||Author and Puzzle-solver|
|21||Thomas Crosse||heteronym/proto-heteronym||English epic character/occultist, popularised in Portuguese culture|
|22||I. I. Crosse||heteronym/para-heteronym||----|
|23||David Merrick||heteronym/semi-heteronym||Poet, storyteller and Playwright|
|24||Lucas Merrick||heteronym/para-heteronym||Short story writer, perhaps brother David Merrick|
|25||Pêro Botelho||heteronym/pseudonym||Short story writer and author of Letters|
|26||Abílio Quaresma||heteronym/character/meta-heteronym||A character inspired by Botelho Pêro and author of short detective stories|
|27||Inspector Guedes||character/meta-heteronym?||A character inspired by Botelho Pêro and author of short detective stories|
|28||Uncle Pork||pseudonym/character||A character inspired by Botelho Pêro and author of short detective stories|
|29||Frederick Wyatt||alias/heteronym||Poet and prose writer (in the English language)|
|30||Rev. Walter Wyatt||character||Possibly brother of Frederick Wyatt|
|31||Alfred Wyatt||character||Another brother of Frederick Wyatt/a resident of Paris|
|32||Maria José||heteronym/proto-heteronym||Wrote and signed "A Carta da Corcunda para o Serralheiro"|
|33||Chevalier de Pas||pseudonym/proto-heteronym||Author of poems and letters|
|34||Efbeedee Pasha||heteronym/proto-heteronym||Author of humoristic "Stories"|
|35||Faustino Antunes/A. Moreira||heteronym/pseudonym||Psychologist, author of "Ensaio sobre a Intuição"|
|36||Carlos Otto||heteronym/proto-heteronym||Poet and author of "Tratado de Lucta Livre"|
|37||Michael Otto||pseudonym/para-heteronym||Probably brother of Carlos Otto who was entrusted with the translation into English of "Tratado de Lucta Livre"|
|39||Horace James Faber||heteronym/semi-heteronym||short story writer and essayist (in English)|
|40||Navas||heteronym/para-heteronym||Translated Horace James Faber in Portuguese|
|41||Pantaleão||heteronym/proto-heteronym||Poet and prose|
|42||Torquato Fonseca Mendes da Cunha Rey||heteronym/meta-heteronym||Deceased author of a text, Pantaleão decided to publish|
|43||Joaquim Moura Costa||proto-heteronym/semi-heteronym||satirical poet, Republican activist, member of "O PHOSPHORO"|
|44||Sher Henay||proto-heteronym/pseudonym||Compiler and author of the preface of a sensationalist anthology in English|
|45||Anthony Gomes||semi-heteronym/character||Philosopher, author of "Historia Cómica do Affonso Çapateiro"|
|46||Professor Trochee||proto-heteronym/pseudonym||Author of an essay with humorous advice for young poets|
|47||Willyam Links Esk||character||Signed a letter written in English on 13/4/1905|
|48||António de Seabra||pseudonym/proto-heteronym||Literary critic|
|49||João Craveiro||pseudonym/proto-heteronym||Journalist, follower of Sidónio Pereira|
|50||Tagus||pseudonym||Collaborator in "NATAL MERCURY" (Durban, South Africa)|
|51||Pipa Gomes||draft heteronym||Collaborator in "O PHOSPHORO"|
|52||Ibis||character/a pseudonym||A character from Pessoa's childhood, accompanying him until the end of his life/also signed poems|
|53||Dr. Gaudencio Turnips||proto-heteronym/pseudonym||Director of "O PALRADOR", English-Portuguese journalist and humorist|
|54||Pip||proto-heteronym/pseudonym||Poet, humorous anecdotes. Predecessor of Dr. Pancrazio|
|55||Dr. Pancrazio||proto-heteronym/pseudonym||Storyteller, poet and creator of charades|
|56||Luís António Congo||proto-heteronym/pseudonym||Collaborator in "O PALRADOR", columnist and presenter of Lanca Eduardo|
|57||Eduardo Lance||proto-heteronym/pseudonym||Luso-Brazilian poet|
|58||A. Francisco de Paula Angard||proto-heteronym/pseudonym||Collaborator in "O PALRADOR", author of "textos scientificos"|
|59||Pedro da Silva Salles/Zé Pad||proto-heteronym/alias||Author and director of the section of anecdotes at "O PALRADOR"|
|60||José Rodrigues do Valle/Scicio||proto-heteronym/alias||"O PALRADOR", author of charades and 'literary manager'|
|61||Dr. Caloiro||proto-heteronym/pseudonym||"O PALRADOR", reporter and author of "A pesca das pérolas"|
|62||Adolph Moscow||proto-heteronym/pseudonym||"O PALRADOR", novelist, author of "Os Rapazes de Barrowby"|
|63||Marvell Kisch||proto-heteronym/pseudonym||Author of a novel announced in "O PALRADOR", called "A Riqueza de um Doido"|
|64||Gabriel Keene||proto-heteronym/pseudonym||Author of a novel announced in "O PALRADOR", called "Em Dias de Perigo"|
|65||Sableton-Kay||proto-heteronym/pseudonym||Author of a novel announced in "O PALRADOR", called "A Lucta Aérea"|
|66||Morris & Theodor||pseudonym||"O PALRADOR", author of charades|
|67||Diabo Azul||pseudonym||"O PALRADOR", author of charades|
|68||Parry||pseudonym||"O PALRADOR", author of charades|
|69||Gallião Pequeno||pseudonym||"O PALRADOR", author of charades|
|70||Urban Accursio||alias||"O PALRADOR", author of charades|
|71||Cecília||pseudonym||"O PALRADOR", author of charades|
|72||José rasteiro||proto-heteronym/pseudonym||"O PALRADOR", author of proverbs and riddles|
|73||Nympha Negra||pseudonym||"O PALRADOR", author of charades|
|74||Diniz da Silva||pseudonym/proto-heteronym||Author of the poem "Loucura" and collaborator in "EUROPE"|
|75||Herr Prosit||pseudonym||Translator of 'O Estudante de Salamanca' by Espronceda|
|76||Henry More||proto-heteronym||Author and prose writer|
|78||J. M. Hyslop||character?||Poet|
Other writers and their heteronyms 
- Søren Kierkegaard - Had more than a dozen heteronyms with distinct biographies and personalities.
- David Solway, Canadian writer, writing as Andreas Karavis.
- Kent Johnson, American scholar and poet writing as Araki Yasusada.
- Robin Skelton, Canadian poet and occultist, writing as French surrealist Georges Zuk.
- B.H. Fairchild, American poet, writing as Roy Eldridge Garcia.
- Romain Gary, French writer, writing as Émile Ajar, Fosco Sinibaldi, Shatan Bogat.
- Antoine Volodine, French writer, writing as Elli Kronauer, Manuela Draeger, Lutz Bassman.
- Brian O'Nolan writing as Myles na gCopaleen.
- Arnon Grunberg writing as Marek van der Jagt.
- ZENITH, Richard (2002), The Book of Disquiet, Penguin Classics, 2002.
See the introductory parts in:
- Fernando Pessoa & Co: Selected Poems, edited and translated by Richard Zenith, Grove Press, 1999
- The Selected Prose of Fernando Pessoa, edited and translated by Richard Zenith, Grove Press, 2002
- The Book of Disquiet, edited and translated by Richard Zenith, Penguin classics, 2003