Must one's "primary" family name in the U.S. be the first in order?

Question

When someone who was born and given their name in a country that uses multiple family names lives in the U.S., are there rules as to what their "official" last name must be?

I heard an immigration officer use a first family name as a "last name", which caused confusion, in this case, to the point where the person being called did not realize it was them that was being referred to.

This is because this person has a Portuguese-style name, where a full name like "João Carlos Fernandes Gonçalves Gomes" refers to a person with the given names "João Carlos" and the family names "Fernandes Gonçalves Gomes". Their father's last-in-order family name was most likely "Gomes", and when a short name is called for, they're probably known as "João Gomes". However, in this case, the immigration officer would have asked for a "Mr. Fernandes".

Was this a simple confusion with Spanish-style surnames, where a "Juan Carlos Fernández Gomez" would be most commonly known as "Juan Fernández"? Or is this a general rule in the U.S., that long last names are always shortened by choosing the first part of it?

Can poor João write his name on official documents as "João C. Gomes" (or another choice of middle initial) without applying for a name change, or is that strictly incorrect in the U.S.? He had thought it'd be simple when he heard the terms "first name" and "last name"—"João" is literally the first, and "Gomes" the last, in order, in his full name.

Answer 1

Joao Gomez would, in this case, be correct. The father's surname is used in US documents. Other names are included in the Middle Names category.

Answer 2

When someone who was born and given their name in a country that uses multiple family names lives in the U.S., are there rules as to what their "official" last name must be?

Although the question is directly specifically at the US, the basic answer applies in all countries, because there is one directly relevant universal law: Sod's law.

If you have two documents which use different forms of your name, at some point you will run into a bureaucrat who will demand additional proof that they refer to the same person.

Therefore, on all official forms, you should use your name as it is written on your primary ID document. João should write "Fernandes Gonçalves Gomes" in the "last name" field (unless his passport omits some of those names).

Note that this applies not only to direct interactions with governmental bodies, but also to any documents which might be relevant in future interactions with governmental bodies. The one which comes to mind at the moment is certificates of education, which might be necessary in future applications for working visas.

I heard an immigration officer use a first family name as a "last name", which caused confusion, in this case, to the point where the person being called did not realize it was them that was being referred to.

This was probably a simple confusion with Spanish-style surnames. "Anglo-Saxon" culture also has double-barrelled surnames, and it's likely that the immigration officer would have called e.g. a Mr Smith Jones using both parts of the surname.

João Gomes is going to have to learn which ways his name might get mangled in his host country and be alert for all of them. That is, again, not specific to the US. As someone with an English name (first name, middle name, one surname) living in Spain, when I'm waiting to be called I keep an ear out for anything which could be an attempt at pronouncing Mr John.