Alberto Caeiro was one of the alter egos used by the eccentric Portuguese poet Fernando Pessoa (1888 – 1935).
The main difference between Pessoa and his contemporaries was that he readily published his poems under the names of his various alter egos. He invented the identity of Alberto Caeiro during 1914. By that time he had decided to dedicate his life to writing poetry, his income supplemented by an inheritence as well as translation work.
Although Pessoa wrote extensively in English and French he decided that all the poems published in the name of Caeiro would be entirely in his mother tongue of Portuguese.
Caeiro was given a complete biography as if he had actually existed, supposedly being born on 16 April 1889 in the city of Lisbon. The two main collections published under the name of Alberto Caeiro were The keeper of Sheep and The Shepherd In Love.
Kaufman H Is the Minor Essential?: Contemporary Portuguese Fiction and Questions of Identity, Symphony Vol. 5, No ½ special issue: Reflecting Europe (1997) University of Nebraska, pp. 167 – 182
Pessoa F A Little Larger Than The Entire Universe Selected Poems Edited & Translated by R Zenith (2006)