Rayen Simson entered his first major tournament in 1995 where he competed in the inaugural Shoot Boxing World Tournament 1995 in Osaka, Japan, along with eight other fighters from across the world. The young Simson was unable to make much of an impact at the event, losing in the quarter final stage after a tough five round battle with Thai Bovi Chorwaikan. He returned to Europe where he won the W.P.K.L. European title and went on an impressive winning streak, culminating in a victory over the legendary Ramon Dekkers in a memorable match in Roosendaal in 1997. Simson recovered from two knockdowns to defeat Dekkers by technical knockout at the end of the second round. His confidence high Simon headed back to Japan to participate in the Shoot Boxing World Tournament 1997, which he had qualified for by beating the ’95 finalist Roni Lewis the previous year. Simson defeated ’95 champion Hiromu Yoshitaka in the semi finals before defeating Mohamed Ouali in the final by unanimous decision to claim his first major title. Over the next few years he would win a number of fights before defeating Najim Ettouhlali in 1997 for the W.P.K.L European title and Hassan Ettaki in 1998 for the W.P.K.L. World title. In 1999 Simson faced multiple Muay Thai world champion and living legendIvan Hippolyte in the first of their two fights, inflicting a rare defeat on Hippolyte after five gruelling rounds. The two fighters would meet again the next year in a rematch in what would be Hippolyte's last ever match. This time Simson was unable to defeat Hippolyte, being knocked down in the third before withdrawing from the fight in the fourth due to a leg injury. Simson would go back to winning ways at the start of the millennium, between 2000 and 2002 he won the Dutch national Muay Thai title, the I.K.B.O World title and the 72.6 kg version of his W.P.K.L World title against Ashwin Balrak. Towards the end of 2002 he faced Joerie Mes in Haarlem, Netherlands. Simson lost by technical knockout after being outworked by the relentless Mes over four rounds. This match would spark the beginning of a fierce rivalry between the two men – they would fight two more times, with Mes being something of a nemesis to Simson, winning all three times. In 2003 he would win the World Kickboxing Network World title in his native Suriname before making his K-1 debut at the K-1 Holland Grand Prix 2003, losing by decision to Perry Ubeda. He would meet Ubeda several years later in 2005 in a losing bid for the WorldFull Contact Association 72.5 kg title. In 2006 Simson would return to K-1 at the K-1 MAX Netherlands 2006 eight man tournament where the prize for winning was a reserve fight at the forthcoming K-1 MAX World Final. Simson booked his flight to Tokyo by defeating Faldir Chahbari in the final by extra round decision. He faced Artur Kyshenko at the K-1 World MAX 2006 Final but lost by third round majority decision, although the result would not mean overmuch as no injuries occurred during the final. At the end of the year and after a nine-year absence, Simson was invited back to the S-Cup to take part in another reserve fight at the Shoot Boxing World Tournament 2006. The ’97 S-Cup winner won his bout against Koichi Kikuchi but would not have the chance to proceed as there were no injuries. This event would be his last major international tournament. Between 2006 and 2009 Simson would enter several small tournaments in Europe, winning the TaoThai "Cosa Nostra" Kombat League in Italy. By this point, despite the odd victory, age was taking its toll and his career was winding to a close. In 2009 he faced Eugene Ekkelboom in Montego Bay, Jamaica for Eugune’s W.M.C. Super Middleweight World title in what would be Simson's last title fight. Simson lost the bout by technical knockout, suffering an arm injury at the start of the fourth. In 2010 he had his final match at It's Showtime 2010 Amsterdam against Şahin Yakut, who was a replacement for his initial opponent Khalid Bourdif, who Simson had handpicked for his retirement match. Simson was unable to finish his career with a win, battling valiantly but ultimately losing by unanimous decision.
