Bhutan's early history was cloaked within mythology and obscurity. In the early years, the outside world had no name for Bhutan, for its mighty towering perimeters had shielded it like an impenetrable mystery. Yet, locals have had a name which they still refer fondly as Druk Yul (literally " The Land of the Thunder Dragon ").
About the turn of the 12th century A.D., the Drukpa Kagyupa School was established and gained prominence as the main form of Buddhism till today. On December 17, 1907, Ugyen Wangchuck was elected as the head of state Druk Gyalpo (Dragon King), and in 1910, he signed the Treat of Punakha with the British. This meant if Bhutan accepted external advice in their external relations, British India would not interfere with their internal matters.
In 1926, after Ugyen Wangchuck passed on, his son Jigme Wangchuck became the next Druk Gyalpo, and as India gained independence in 1947, Bhutan was recognized as an independent nation. Succeeded by his son Jigme Dorji Wangchuck in 1952, Bhutan began a series of meticulously organized development which saw Bhutan emerging from its solitude and joining the United Nations in 1971. Following that in 1972, Jigme Singye Wangchuck ascended the throne and modernized the education system and governance. Also, he oversaw the urbanization in rural areas and introduced hydroelectricity and tourism. It was that time when the philosophy of Gross National Happiness was initiated, and in 2006 before the promulgation of the new constitution of Bhutan, his son Jigme Khesar Namgyel Wangchuck succeeded as the King.
Source: Michigan State University