BANGKOK — Prem Tinsulanonda, an army commander in chief who served as prime minister of Thailand for two terms and later became the head of the influential Privy Council of the king, died on Sunday in Bangkok. He was 98.
His death was confirmed by Chai Chidchob, a senior lawmaker in the National Assembly, which observed a minute of silence in Mr. Prem’s honor. Mr. Chai did not specify the cause of death.
Without facing a general election, Mr. Prem held the prime minister’s post with the backing of the king from 1980 to 1988, shuffling cabinets five times and weathering two coup attempts.
He left much of the day-to-day administration to bureaucrats, weakening the influence of political parties and the military.
As prime minister and in his subsequent close connection with the palace, Mr. Prem often acted as a proxy for King Bhumibol Adulyadej, a constitutional monarch who had no direct political power but enormous moral influence.
“The king trusted Prem absolutely,” wrote the political scientist Duncan McCargo, “seeing him as an incorruptible figure who shared his soft and understated approach, but who was a skilled alliance-builder and wielder of patronage.”
Mr. Prem never joined a political party, and his power as prime minister rested on the support of the king, who backed his selection for office by Parliament and protected him from political challenges.
During the “April Fools’ Day” coup attempt in 1981 by a group of officers known as the Young Turks, Mr. Prem hurried to the northeastern city of Korat, where the royal family was in residence. This demonstration of royal favor won him the support of regional military commanders, and the rebellious officers were quickly rounded up.
Using horse racing as a metaphor, he once described the king as the “owner” of Thai political power, which is wielded by others on his behalf.
“In this country we consider that we belong to the king,” he said in 2006, shortly before supporters of the monarchy staged a coup.
“In horse racing they have the stable, and the owner of the stable owns the horse,” he said. “The jockey comes and rides the horse during the race, but the jockey does not own the horse.”
On the Privy Council, which he headed beginning in 1998, Mr. Prem was a mainstay of a ruling class that included conservative royalists, the military, senior bureaucrats and big business. He was a powerful player behind the scenes even into his 90s, particularly as the king’s health failed.
After the king’s death on Oct. 13, 2016, Mr. Prem served as regent pro tempore until the installation of the new king, Maha Vajiralongkorn Bodindradebayavarangkun, who reappointed him to head the council.
Thailand’s hierarchical order was shaken in early 2001 by Thaksin Shinawatra, a telecommunications billionaire who was elected prime minister by appealing to the aspirations of a politically marginalized, mostly rural poor majority.
With strong electoral backing, Mr. Thaksin began a populist movement that challenged the primacy of the monarchy and military as well as the scope of Mr. Prem’s power.
When Mr. Thaksin was ousted in the 2006 coup, his supporters accused Mr. Prem of being the mastermind and controlling the military-backed junta that took office, a charge the junta denied.
In a widely reported speech at the Naval Academy before the coup, Mr. Prem seemed to be referring to Mr. Thaksin when he said: “Only good people have ethics and morals. Bad people don’t. People who work in public office or those who are commanders or leaders, in particular, must embrace ethics and morality; otherwise things will collapse.”
Prem Tinsulanonda was born on Aug. 26, 1920, in Songkhla Province in southern Thailand, one of eight children of Bueng Tinsulanonda, the warden of the Songkhla prison, and Ord Tinsulanonda. He remained single throughout his life and once described himself as married to the army.
Throughout his career Mr. Prem benefited from a reputation for honest dealing, untainted by the scandals and corruption that characterize much of Thai politics.
According to his website, he studied at military academies including the United States Army Armor School at Fort Benning, Ga. He enlisted in the military as a platoon leader in the Armor Department, rising through the ranks to become a general and commander in chief of the Royal Thai Army in 1978.
He entered politics and served in the Senate and National Assembly before being named deputy minister of the interior and then minister of defense in 1979 in the cabinet of Prime Minister Kriangsak Chamanand.
After taking power in 1980, he retained control of the military as minister of defense. Early in his administration, he offered amnesty to members of the Communist Party of Thailand, which had waged a jungle insurgency. Many Communist members, including thousands of students, returned home, helping to bring the guerrilla movement to an end.
Under political pressure, Mr. Prem dissolved Parliament and stepped down as prime minister in April 1988, declaring, “I have had enough.” Later that year, the king appointed him to the Privy Council.
Mr. Prem’s last public act was early this month at King Maha Vajiralongkorn’s official coronation, where he was one of eight people to pour holy water on the king.