Ong Teng Cheong is not the first Elected President of Singapore but Wee Kim Wee is.
Jack Lee Tsen-Ta, an assistant professor at the Singapore Management University (SMU)’s School of Law has explained why on the Singapore Public Law website.
This is so as the Singapore Parliament amended the constitution in January 1991 to allow for the direct election of the president, who could veto civil service appointments and the use of government reserves.
The amendment was carried out during Wee’s second term in office.
Wee was then the fourth president of Singapore from September 1985 to September 1993.
The Elected Presidency scheme as it exists today was introduced in 1991. The Government’s intention was to enable the President to act as a check on a future rogue government.
The office of President was transformed into one directly elected by the people to give the President moral authority to disapprove of government decisions, if need be.
We might assume the first person to exercise discretionary powers was Ong Teng Cheong, as he won the inaugural presidential election in 1993.
In fact it was Wee Kim Wee who was the first one to do so, due to a special provision – Article 163(1) – inserted into the Constitution when the Elected Presidency scheme was introduced:
The person holding the office of President immediately prior to 30th November 1991 shall continue to hold such office for the remainder of his term of office and shall exercise, perform and discharge all the functions, powers and duties conferred or imposed upon the office of President by this Constitution as amended by the Constitution of the Republic of Singapore (Amendment) Act 1991 (Act 5 of 1991) […], as if he had been elected to the office of President by the citizens of Singapore […]
The provision was carefully worded to avoid deeming Wee Kim Wee as having been elected, so although he exercised all the discretionary powers of an elected President, the first truly elected President was Ong Teng Cheong.
However, others have noted that the common understanding of "elected president" is common enough to enjoy widespread currency for it to be printed in the book, Men In White, which is about the People's Action Party: