Who was the leader of the Others?

Benjamin Linus was the leader of the Others on Lost.

Ben first appears to the survivors under the false name Henry Gale, but his identity is eventually exposed. He leads the Others, a group of long-term inhabitants of the island, and becomes one of the series' principal antagonists. His power comes from a combination of manipulation, secrecy, political skill, and his claimed ability to understand the island's wishes.

Ben's rise is tied to the Dharma Initiative and the island's older inhabitants. As a child, he moves to the island with his father, Roger Linus, who works for Dharma. Ben later joins the group known as the Hostiles, helps destroy the Dharma community, and eventually exiles Charles Widmore before assuming leadership of the Others.

The answer can be confusing because several characters hold influence over the island. Richard Alpert serves as Ben's trusted second-in-command, while Jacob is the island's long-standing protector and spiritual authority. Charles Widmore is a former leader and rival, not the leader during most of the main storyline. By the end of the series, Ben no longer leads the Others; instead, he becomes an adviser to Hurley, the new Island protector.