Who were Fernando Pessoa's main heteronyms?

Context: Fernando António Nogueira Pessoa was a Portuguese poet, writer, literary critic, translator, publisher, and philosopher, described as one of the most significant literary figures of the 20th century and one of the greatest poets in the Portuguese language. He also wrote in and translated from English and French.

Pessoa was a prolific writer, and not only under his own name, for he created approximately seventy-five others, of which three stand out, Alberto Caeiro, Álvaro de Campos, and Ricardo Reis. He did not call them pseudonyms because he felt that this did not capture their true independent intellectual life and instead called them heteronyms. These imaginary figures sometimes held unpopular or extreme views.

Pessoa's earliest heteronym, at the age of six, was Chevalier de Pas. Other childhood heteronyms included Dr. Pancrácio and David Merrick, followed by Charles Robert Anon, a young Englishman who became Pessoa's alter ego. In 1905/7, when Pessoa was a student at the University of Lisbon, Alexander Search took the place of Anon. The main reason for this was that, although Search was English, he was born in Lisbon, as was his author. But Search represents a transition heteronym that Pessoa used while searching to adapt to the Portuguese cultural reality. After the republican revolution, in 1910, and consequent patriotic atmosphere, Pessoa created another alter ego, Álvaro de Campos, supposedly a Portuguese naval and mechanical engineer, who was born in Tavira, hometown of Pessoa's ancestors, and graduated in Glasgow. Translator and literary critic Richard Zenith notes that Pessoa eventually established at least seventy-two heteronyms. According to Pessoa himself, there are three main heteronyms: Alberto Caeiro, Álvaro de Campos and Ricardo Reis. Pessoa's heteronyms differ from pen names, because they possess distinct biographies, temperaments, philosophies, appearances, writing styles and even signatures. Thus, heteronyms often disagree on various topics, argue and discuss with each other about literature, aesthetics, philosophy, etc.

Answer: Fernando Pessoa created approximately seventy-five heteronyms, of which three stand out, Alberto Caeiro, Álvaro de Campos, and Ricardo Reis.
Pessoa's heteronyms differ from pen names, because they possess distinct biographies, temperaments, philosophies, appearances, writing styles and even signatures.