The Ten Dons (十老頭, Jūrōtō), also called the Ten Mafia Dons, is the nickname for the group of the 10 Mafia leaders of the 10 territories into which the six continents of the Hunter × Hunter world are divided. In reality they don't act by themselves but use their special bodyguards, the Shadow Beasts, a group of the best 10 fighters within the Mafia.
Yorknew City arc
After a large number of Mafia members and auction clients in Yorknew City are massacred by the Phantom Troupe, the Ten Dons send the Shadow Beasts to deal with them, not knowing who they are. After the Shadow Beasts are killed subsequently, they put large bounties on the Troupe's heads and hire professional assassins, including Zeno and Silva, to eliminate the Troupe's members. The plan failed because the Troupe's leader Chrollo Lucilfer hired other members of the Zoldyck Family Maha, Illumi and Kalluto to assassinate the Ten Dons, a mission that is accomplished before Zeno and Silva were able to assassinate Lucilfer. Because of their deaths, Zeno and Silva no longer consider Lucilfer to be a target and leave Yorknew City.