Wesley Barbossa So (born October 9, 1993) is an Filipino and American chess grandmaster, a three-time U.S. Chess Champion, and the first World Fischer Random Chess Champion. He is also a three-time Philippine Chess Champion. On the March 2017 FIDE rating list, he was ranked number two in the world and had an Elo rating of 2822, making him the fifth-highest-rated player in history.

In 2019, So said his favorite form of chess is chess960 (also known as Fischer random chess). Later that year, So became the inaugural World Fischer Random Chess Champion after defeating Magnus Carlsen to win the FIDE World Fischer Random Chess Championship.

A former chess prodigy, So became the youngest player to pass a 2600 Elo rating in October 2008, breaking the record previously held by Carlsen. This record has since been broken by Wei Yi, John M. Burke and Yağız Kaan Erdoğmuş. In early 2013, So passed 2700 and in January 2017 he became the 11th player to pass 2800 Elo.

So represented the Philippines until transferring to the United States in 2014. He won the 2015 Bilbao Chess Masters, the 2016 Grand Chess Tour title after claiming victory in the Sinquefield Cup and London Chess Classic, the 2017 Tata Steel Masters, the 2021 Grand Chess Tour, and the 2025 Sinquefeld Cup. He represented the US on board 3 at the 42nd Chess Olympiad, winning team and individual gold.

So was born in the Philippines in 1993 to Filipino-Chinese William and Eleanor So. He has one older sister, Wendelle Barbossa So, and one younger sister, Wilma Barbossa So. So attended the Jesus Good Shepherd School and Saint Francis of Assisi College in Bacoor.

So was at the age of ten years old when he began competing in junior tournaments. So took first place at the 2003 Philippine National Chess Championships in the U-10s section. As a junior player, he also competed in various sections of World Youth Chess Championships, finishing 19th in the U-10s in 2003, 13th in the U-12s in 2004 and fourth place in the U-12s in 2005. He also took part in the ASEAN Open U-10s in 2004, securing individual golds in the standard and rapid sections along with team silver medals in the standard and rapid along with winning individual golds in the standard, rapid and blitz sections in the U-12s in 2005.

So made his tournament debut at the Nice International Open in August 2005, finishing in sixteenth place (from 159) with 4/7. He also completed three International Master norms in the space of four months, becoming the youngest Filipino to achieve that status after scoring 5/9 at the Dubai Open, 5½/9 at the San Marino Open and 6½/11 at the Dato Arthur Tan Malaysia Open. During this period, So made his first Olympiad appearance on second reserve board at the 37th Chess Olympiad held in Turin in 2006.

So's form continued with 5½/9 at the Calvia Open, his first GM-norm with 7/9 at the Bad Wiessee Open, tying for sixth with 4/8 at the GMA Presidents Cup in Parañaque and ended 2006 by scoring 6/9 at the Singapore Masters. In January 2007, So qualified for the Chess World Cup 2007 via the Zonal tournament held in Phú Quốc, Vietnam, scoring 5½/9. Between January 2006 and April 2007, So had increased his FIDE rating by 303 points to 2519.