The Spanish word 'protagonista' comes from Ancient Greek 'πρωταγωνιστής' (protagonistes), which literally meant 'first actor' or 'protagonist'. This Greek word was formed by combining two elements: 'πρῶτος' (protos) meaning 'first', and 'ἀγωνιστής' (agonistes) meaning 'combatant' or 'competitor'.

In ancient Greek theater, the 'protagonistes' was literally the principal actor who played the main role in a drama. Over time, this theatrical term evolved to refer more generally to the main character of any story, which is how we use it today in Spanish.

The word 'agonía' in Spanish, meaning 'agony' or 'anguish', shares a connection with 'protagonista' through the Greek root 'agon-' which related to struggle or contest. Another related Spanish word is 'antagonista' (antagonist), which uses the same '-agonista' ending but with the prefix 'ant-' meaning 'against' instead of 'prot-' meaning 'first'.

English speakers will recognize the cognate word 'protagonist', which is identical in meaning to the Spanish 'protagonista'. Other related English words include 'agony' and 'antagonist'. The 'proto-' prefix appears in many English words like 'prototype' (first model) and 'protocol' (first sheet or first draft), all carrying the sense of 'first' or 'primary' from the Greek 'protos'.