King George Tupou V of Tonga, who has died aged 63 after suffering from cancer, was, like his father, Taufa'ahau Tupou IV, crown prince for more than 40 years before succeeding to the throne. A pragmatic ruler, he accelerated democratic reforms in the South Pacific archipelago of more than 170 islands to the north-east of New Zealand, around 50 of them inhabited by a total population of 106,000.
When, in 2006, George Tupou became king, he inherited a troubled and impoverished state. Few expected that he could gain his subjects' affection to any extent approaching his two immediate predecessors; his grandmother was the popular Queen Salote.
Two months after his father's funeral, pro-democracy demonstrations led to riots in the commercial centre of the capital, Nuku'alofa, eight deaths and the destruction of buildings and property. George Tupou postponed his coronation. Just before it eventually took place, in August 2008, attended by heads of state and politicians from around the globe, he announced radical changes, renouncing most of his powers and establishing a timetable for democratic parliamentary elections.
Tongan society is highly stratified, with the monarchy, comprising three royal lines united in the Tupou dynasty, the 33 title-holding nobles, and the commoners. After hard-fought civil wars in the 18th and 19th centuries, the Tupou dynasty consolidated power through skilful alliances and manipulation of missionary support. Tonga avoided annexation through a treaty of friendship with Britain in 1900.
Tongan monarchs ruled benevolently, but still set the tone of governance, and through the 1875 constitution chose a portion of the cabinet, with representatives elected by the nobles and the commoners. Tupou had been foreign minister (1979-98) and, along with his siblings, an innovator, establishing electricity and mobile phone enterprises.
Educated in New Zealand at King's college, Auckland, and in Britain at the Leys school, Cambridge, he was fluent in eight languages. After studying international law at Oxford University, he graduated from Sandhurst Military Academy, returning to Tonga in 1969.
He was portrayed as distant from his people and absorbed with an opulent, international lifestyle, the personal trappings of his princely role, and eccentricities such as acquiring two London black cabs for his personal use – he was a fervent Anglophile – and the wearing of elaborate military uniforms.
However, the necessity for democratic reform was impressed on him not only by the 2006 riots, but also by the Royal Commission that followed the sinking of the Princess Ashika ferry in 2009 with the loss of 74 lives, revealing endemic corruption and laxity. Its report came in 2010, the year that the proportion of directly elected people's representatives was for the first time increased to a majority in the parliament. Ill-health may also have encouraged him to speed political reforms.
The king did not marry. He is survived by a daughter, his younger brother, Crown Prince Tupouto'a Lavaka, his mother and his sister.
• George (Siaosi) Tupou V, King of Tonga, born 4 May 1948; died 18 March 2012.