What do you used to address someone formally in Spanish?

In colonial periods, people said: "vos", for the polite pronoun "usted" did not exist before the 18th century. Thus people addressed others this way:

¿Quién sois vos? --- Who are you? (formal singular, both genders)

¿Quiénes sois vosotros, as? (both formal and informal plural)

The verb, in classical standard Spanish is conjugated the same for both "vos" and "vosotros, as": Vos / vosotros tenéis, estáis, decís, queréis, inquirís, intentáis...

Later, during the middle of the 18th century, roundabout, the "voseo" or use of "vos" became unpopular for educated people, giving way to the modern and polite "vuestra merced", changing to "vuesarced > voacé > vusted > and finally usted", a pronoun that conjugates the verb in the third person, despite belonging to the second person:

Es usted muy amable / ustedes sonmuy amables --- you are so kind

As "usted" and "ustedes" are very polite, these pronouns became more extensive, especially in Spanish America, and substituted the use of "vosotros" by "ustedes". Thus, in Spanish America, people refer to other as "ustedes". Nonetheless, Spain kept both treatment pronouns to make difference between polite contexts (use of "ustedes") and informal ones (use of "vosotros").

Ustedes son mis amigos (Spanish America, informal) / (vosotros) sois mis amigos (Only in Spain, informal) --- you are my friends

Sean bienvenidos, señores (Spain and Spanish America, formal) --- Welcome, gentlemen.

In classical literature: The Bible, the Iliad, the Odissey and this sort of texts, the use of "vosotros, as" and "tú" is mainly found, in order to keep the environment of those oeuvres as if they were lived by the reader at the moment of reading them.