Hassan-i Sabbāh

Hassan-i Sabbāh (1050s - 1124) was the leader of the Assassin Brotherhood in the Levant during the late 11th and early 12th century.

Under his leadership, the Assassins in the Levant became a public organization, attempting to make the people realize that they were not alone in their fight against oppression, and to make them stand up for themselves - though the Assassins' practices remained unknown.

Source

 * Assassin's Creed Encyclopedia