Hassan-i Sabbāh

Hassan-i Sabbāh (1050s - 1124) was a Grand Master of the Assassin Order during the late 11th and early 12th century.

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

Source

 * AC Timeline