Elizabeth II is the world's oldest reigning monarch.
Elizabeth II . She is the world 's oldest reigning monarch as well as Britain 's longest-lived . In 2015 , she surpassed the reign of her great-great-grandmother , Queen Victoria , to become the longest-reigning British monarch and the longest-reigning queen regnant and female head of state in world history . In October 2016 , she became the longest currently reigning monarch and head of state following the death of King Bhumibol Adulyadej of Thailand .