Alberto Caeiro was born in Lisbon, in 1889 and died in 1915, but lived most of his life in the country with an old great aunt because he was orphaned from a young age. He had blonde hair and blue eyes. He finished his primary school education and had no profession.
How did this heteronym come about? Fernando Pessoa tells us “one day he decided to play a trick on Sá-Carneiro — so he drew up a bucolic poet, of the complicated kind and had them meet, I can’t remember how, in some sort of real context. I spent some days trying to formulate the poet but achieved nothing. One day, on the verge of giving up – March 8th 1914 – I approached a high chest of drawers and, began to write something down on a piece of paper, while standing, as I like to do, whenever possible. And so, taken over by some strange, indescribable kind of trance, I wrote 30 something poems in one stretch. That was the most triumphant day of my life and I will never experience another like it. I began with the title The Keeper of Flocks. And what followed was the birth of someone within me, whom I immediately named Alberto Caeiro. Please excuse the absurdity of the phrase: my master will appear within me. But that was my immediate sensation.”
When Fernando Pessoa writes as Caeiro, he claims to do so “in pure and unexpected inspiration, not knowing or guessing what he will write.”

Source: Fernando Pessoa’s Letter to Adolfo Casais Monteiro, January 1935, in Correspondência 1923-1935, ed. Manuela Parreira da Silva, Lisbon, Assírio & Alvim, 1999.