The office of Prime Minister dates back to 1959 and was appointed at first by the Governor of Singapore then the Yang di-Pertuan Negara (vice-regal head of state), when Singapore achieved self-governance as the State of Singapore within the British Empire. The title of Prime Minister remained unchanged after the merger with the Federation of Malaya, Sarawak and British North Borneo, while Singapore was a state in the Federation of Malaysia from 1963 to 1965, and after independence in 1965.
Lee Kuan Yew was the first prime minister of Singapore from 1959 to 1990 and retired on 26 November 1990. Lee was succeeded by Goh Chok Tong and was conferred the title of Senior Minister in the Prime Minister's Office. Goh retired on 12 August 2004 and was succeeded by Lee Kuan Yew's son Lee Hsien Loong. Goh was appointed Senior Minister, and the elder Lee Minister Mentor.