There are many ways of referring to the person born on December 19, 1842 in Francisio di Campodolcino in Italy, ordained in 1866, died in Como Italy on October 24, 1915, and was beatified by Pope Paul VI on October 25, 1964. Let's take a look at these names...
This is the title given to a beatified person. Luigi Guanella was beatified by Pope Paul VI on October 25, 1964. Before this name, one would call him "Venerable Servant of God" which only states that the Apostolic See has recognized the heroicity of his virtues. And before this, his title would have been "Servant of God" without any attachment of the title "Venerable."
These titles are given to a priest. Father and Fr. are common to English-speaking people. "Don" is an Italian title of respect, from donno, literally, lord, from the Latin dominus. "Dom" is the Portuguese version of "Don" and is also used as a title for some monks and canons regular.
All these names are versions of Luigi's first name. According to Bishop Raymond L. Burke, former Bishop of the Diocese of La Crosse, now Archbishop of St. Louis "In Latin, his first name is Aloisius, which makes me think that the translation of his name into English should be Aloysius. The name Luigi in Italian can be translated into English as either Aloysius or Louis. The Latin for Aloysius is Aloisius; the Latin for Louis is Ludovicus." And so, any of these names are proper depending on where you are getting the translation from. I, personally, use Luigi most often simply because it is Italian, and Luigi Guanella was Italian. Just for some interesting facts, the name "Louis" is of German origin meaning "Famous Warrior," the name "Luigi" is of Italian origin meaning "Warrior," and the name "Aloysius" is of German origin meaning "A Warrior."
The last name of Luigi. The Guanella family originated in the northern region of Italy around and in Francisio di Campodolcino where Luigi Guanella lived. Today, there are Guanella's in the United States, Italy, South America, and Australia.