Breakdown of O rei já fora um cavaleiro muito valente.
ser
to be
muito
much / very
um
a / an / some (all forms)
já
already
Questions & Answers about O rei já fora um cavaleiro muito valente.
The word fora usually means outside. How does it function as a verb here?
In this sentence, fora is the Pretérito Mais-Que-Perfeito Simples (simple pluperfect) of the verb ser (to be). It translates to had been. It shares the exact spelling with the adverb fora (outside), but you can tell it is the verb here because it acts as the main action for the subject o rei.
Does fora come from ser (to be) or ir (to go)?
It is ser in this context, but it could be either! Just like in the simple past where foi means both was and went, the simple pluperfect forms of ser and ir are completely identical (fora, foras, fora, fôramos, fôreis, foram). Context tells us which one it is: had been a knight makes sense, whereas had gone a knight does not.
How is fora different from tinha sido?
They mean exactly the same thing: had been. However, tinha sido (the compound pluperfect) is what you will hear in everyday spoken Portuguese. The simple form (fora) is highly literary and is mostly found in books, poetry, or historical texts. It fits this sentence perfectly because a story about a king (rei) and a knight (cavaleiro) is likely from a fairy tale or novel.