Mustache Pete was the name given to members of the Sicilian Mafia who came to the United States (particularly New York City) as adults in the early 1900s.
Unlike the younger Sicilian-Americans known as the "Young Turks", the old guard Mustache Petes had usually committed their first killings in Italy. The most prominent members of this group were Joe "the Boss" Masseria and Salvatore Maranzano. Many of them also had connections with the Sicilian Mafia. The Mustache Petes wanted to maintain Sicilian criminal traditions in their new country and were more interested in working with and exploiting their fellow Italians rather than the public at large. To that end, they opposed their younger members' desire to work with the powerful Jewish and Irish gangs. These younger members wanted to branch out realizing the numerous other ways in which to make their fortunes, but were stifled by the Mustache Petes. This rankled younger caporegimes, such as Lucky Luciano and Vito Genovese.
Luciano and other "Young Turks" in the New York Mafia soon concluded that the Mustache Petes were too set in their ways to see the millions of dollars that working with non-Italian gangsters could bring. During the Castellammarese War, Luciano built a network of younger Mafiosi in both the Masseria and Maranzano camps and secretly intended to assassinate one of the older bosses, then bide their time before killing the other. They eventually decided to kill Masseria, and feigned loyalty to Maranzano until they got a chance to eliminate him as well.
Following this, the newer generation of Italian mobsters reorganized the National Crime Syndicate and founded The Commission, becoming closer to the modern American Mafia known today. It is widely believed that following these events, a purge of older Mafiosi, known as the "Night of the Sicilian Vespers" [allusion to massacre of foreign occupiers], took place across the country, in which most of the remaining Mustache Petes were eliminated, although not in one night. These included Joe Masseria, Salvatore Maranzano, Joseph Siragusa, and Joseph Ardizzone. However, there is no concrete evidence that this happened.
Further reading 
- Raab, Selwyn (2005). Five Families: The Rise, Decline, and Resurgence of America's Most Powerful Mafia Empires. New York: St. Martin's Press. ISBN 0-312-30094-8.