Guillermo Sebastián Coria (born 13 January 1982), nicknamed El Mago (The Magician in Spanish), is a retired professional tennis player from Argentina. He reached a career-high ATP world No. 3 singles ranking in May 2004. Coria achieved his best results on clay, where he won eight of his nine ATP singles titles, and during his prime years in 2003 and 2004 he was considered the "world's best clay-court player." He reached the final of the 2004 French Open, where he was defeated by Gastón Gaudio despite serving for the match twice. In later years, injuries and a lack of confidence affected his game, and he retired in 2009 at the age of 27. Between 2001-2002, he served a seven month suspension for taking the banned substance nandrolone.