Prime Minister of Thailand sixteen out of twenty-nine, including the incumbent General Prayut Chan-o-cha. Military dominance began with the country's second Prime Minister, Phot Phahonyothin, who ousted his civilian predecessor in a coup in 1933. The longest serving Prime Minister was Field Marshal Plaek Pibulsonggram at 14 years, 11 months and 18 days. The shortest was Tawee Boonyaket at just 18 days. Nine were removed by coups d'état, three were disqualified by court order, and eleven resigned from office. The youngest ever to occupy office was M.R. Seni Pramoj at 40 years old. Thailand received its first female prime minister, Yingluck Shinawatra, in 2011.
Acting prime minister is on vacation, or is in ill health. In the early 20th century, when travel by ship was still the norm, it was not uncommon for there to be an acting Prime Minister for months on end. The deputy Prime Minister is usually designated as the acting Prime Minister, although another senior member of the government may fill the role if both the Prime Minister and deputy Prime Minister are unavailable. An acting Prime Minister is required quite frequently – for instance, between 3 December 2007 and 23 February 2009 (during Kevin Rudd's first term), Julia Gillard acted as Prime