There are at least two people in the Bible named Ishmael. The name is sometimes translated into English as Ishmail. The first and most famous was Ishmael, the son of Abraham. Another was the son of Nethaniah, best known for killing Gedaliah, who had been appointed as governor of Judah.
Ishmael, the assassin, is described in Jeremiah 41:1 as being the son of Nethaniah, who was the son of Elishama, who was of the royal lineage. He lived about 2600 years ago, during a time when the Babylonians had conquered the land of Judah (southern Israel). The Babylonians had appointed Gedaliah, who was Jewish, to act as governor on behalf of the Babylonian government.
Ishmael, son of Nethaniah, led 10 men to the town of Mizpah where they assassinated Gedaliah.
Next person in the Bible: Iskah (or Iscah)