Sellapan Ramanathan, DUT (First Class) (born Cellappaṉ Rāmanātaṉ, 3 July 1924) is a Singaporean politician who was the sixth President of the Republic of Singapore. Usually referred to as S. R. Nathan, he was first sworn in on 1 September 1999. In 1999 and 2005, he was elected President in uncontested elections. In 2009, he surpassed Benjamin Sheares to become Singapore's longest-serving President. His 12-year term ended on 31 August 2011.