Rangsan Viwatchaichok (Thai: รังสรรค์ วิวัฒน์ชัยโชค) born January 22, 1979), simply known as Aon is a Thai retired professional footballer who plays as a Midfielder. He previously played for four other club teams in Thailand and Singapore. Rangsan is known for his set pieces. On 11 July 2013, BEC Tero Sasana sacked René Desaeyere and promoted Choketawee Promrut to be the club interim manager. Rangsan hwo was the club captain was also promoted to be the assistant coach. On 9 August 2015, Rangsan was promoted to be the interim manager of BEC Tero Sasana after the removal of Kenny Shiels. He had coached the club for three games before the appoitnment of Manuel Cajuda on 27 August. On 1 December 2015, he was promoted to be the interim manager again after the resignation of Manuel Cajuda. Rangsan managed the club in the last three games of 2015 season with the record of 2 wins and 1 loss. The club set to relegate to Division 1 according to the final standing but still remained in top league after the withdraw of Saraburi F.C. from the competition.