Fidalgo (Portuguese: [fi'ðau], Galician: [fi'ðal]), from Galician fillo de algo and Portuguese filho de algo--equivalent to nobleman, but sometimes literally translated into English as "son of somebody" or "son of some (important family)"--is a traditional title of Portuguese nobility that refers to a member of the titled or untitled nobility. A fidalgo is comparable in some ways to the French gentilhomme (the word also implies nobility by birth or by charge) and to the Italian nobile. The title was abolished after the overthrow of the Monarchy in 1910. It is also a family surname.
The word has the same etymological and historical roots as its Spanish cognate, hidalgo. Although algo generally means "something", in this expression the word specifically denotes "riches" or "wealth" and thus was originally synonymous with rico homem (literally, "a rich man").
As late as the reign of Afonso III (1248-1279), who completed the reconquest of the Algarve, the nobility was not differentiated as it would be later. All nobles, who were the large landowners, were referred to simply by two synonyms, fidalgo and ricos homens. Originally, rico homem referred to the administrative duties entrusted to a noble and fidalgo referred to the inherited status of nobility (in an older parlance, "the nobility of blood"). Below the ricos homens was a descending category of their vassals: the infanções, the knights (cavaleiros), and the squires (escudeiros).
Rico homem and fidalgo reached their current meanings during the reign of John I (1385-1433). Large segments of the nobility did not side with John I in the crisis of 1383-1385 and the subsequent war with Castile; they lost their lands after the new king secured his claim to the throne and were replaced by a new nobility, elevated from previously non-noble families and modeled on the English system. Fidalgo came to be applied to a category analogous to the English "gentleman."
By the start of the fifteenth century, the term infanção fell out of use and "knight" came to mean all those below the ricos homens. Fidalgo began to be emphasized because, in its sense of someone who had inherited nobility, it differentiated the older knights from the growing bourgeoisie that continued to gain access to knighthood through accomplishments in the service of the state.