While the name "Hat Guy" may just seem like a comic relief name and a nifty little narrative technique to make things easier for the voiced quests, it has a deeper root in culture that is often dismissed. I've seen this especially in the Luna arch, where people are irritated at him only being referred to as "hat guy". There is also some hate towards Nahida for giving him a silly name like that. But it seems very intentional to me.

Sumeru is an amalgamation of Medieval India ( Primarily Hindustan era) and Persia and Ancient Egypt. In Old India, immigrants and settlers who were not of much influence would abandon their original names in favour of more local names. This meant new names entirely or an Indianized/Hindustani version of their actual surnames.

This is particularly true for the merchants and refugees that came from Persia. Those who were "nameless" were referred to by their appearance or professions.

This brings us to Hat Guy.

Hat in Hindustani is "Topi".

Guy in Hindustani has many variations, but for this particular instance, it would be "Wala", meaning "man with"

So "man with the hat" would be "Topiwala" in Hindustani ( *ٹوپی والا / टोपी वाला), which IS a genuine surname in India, usually belonging to groups with Persian ancestry.

Hat guy, as a wanderer without a name or identity, was accepted by Sumeru and given a name unique to the culture it represents.

Why did hoyo bother letting us name him if we were never going to use his name anyways?

That's a question I see a lot. I'm sure there are technical reasons for this, like voice recording, but I'd like to point another cultural reference out. In Indian and Persian ( or rather, in all patriarchal countries') academics scholars, teachers, staff and students are mostly called by their surnames. This was true up until my parents generation but is less common now. It was considered very rude for someone to call others by their first name with only the closest of friends or childhood friends using it.

While most of the Sumeru cast is fairly laid back, wanderer does NOT come across as a person who'd let just anyone use his real name. It makes sense then, that the Nod Krai cast only gets introduced to him by the name "Hat Guy".

Though the name might seem out of place to us, I'd like to think that one day, "Hat Guy" too will be a legacy of Sumeru. A name that conveys the pride and prestige of its founder. "House of Hat Guy"

*Pardon my Urdu, I am very much a new learner