As a Brazilian Portuguese speaker: when we're using a series of three placeholder names, it's not uncommon to say or hear: "Fulano, sicrano e beltrano". Some even pronounce "sicrano" as "siclano" (but this is regarded as incorrect). I already knew this word has an Arabic origin, but I didn't know about the controversy of its' etymology.
I'm curious about this word's etymology, but it doesn't seem to be known. I found a wild discussion about it here (tl;dr: someone claimed it was a Greek borrowing without stating which Greek word it was supposed to be from; others said it might be from Egyptian, Akkadian or other exotic stuff — at the end of the day, nothing remotely conclusive).
It was borrowed into Spanish and Portuguese as Fulano (earlier Foão in Portuguese, displaced by the Spanish version).