Question: What is the name of this retired professional tennis player and former World No. 1 who was the defending champion of the 2004 Siebel Open - Singles?

full_context: Document 1: Arthur Ashe: Arthur Robert Ashe Jr. (July 10, 1943 – February 6, 1993) was an American professional tennis player. He won three Grand Slam titles.
Document 2: Pete Sampras: Pete Sampras (born August 12, 1971) is a retired American tennis player widely regarded as one of the greatest in the history of the sport. He was a right-handed player with a single-handed backhand and a precise and powerful serve that earned him the nickname "Pistol Pete". His professional career began in 1988 and ended at the 2002 US Open, which he won, defeating rival Andre Agassi in the final.
Document 3: 2004 Siebel Open: The 2004 Siebel Open was a tennis tournament played on indoor hard courts at the HP Pavilion at San Jose in San Jose, California in the United States that was part of the International Series of the 2004 ATP Tour. The tournament ran from February 9 through February 15, 2004.
Document 4: 2004 Siebel Open – Singles: Andre Agassi was the defending champion but lost in the semifinals to Mardy Fish.
Document 5: Ilie Năstase: Ilie "Nasty" Năstase (] , born 19 July 1946) is a Romanian former world No. 1 professional tennis player, one of the world's top players of the 1970s. He was ranked world no. 1 from 23 August 1973 to 2 June 1974.
Document 6: Andre Agassi: Andre Kirk Agassi ( ; born April 29, 1970) is an American retired professional tennis player and former World No. 1 who was one of the sport's most dominant players from the early 1990s to the mid-2000s. Generally considered by critics and fellow players to be one of the greatest tennis players of all time, Agassi has been called the greatest service returner in the history of the game. Described by the BBC upon his retirement as "perhaps the biggest worldwide star in the sport's history", Agassi compiled performances that, along with his unorthodox apparel and attitude, saw him cited as one of the most charismatic players in history. As a result, he is credited for helping to revive the popularity of tennis during the 1990s.
Document 7: Stefan Edberg: Stefan Bengt Edberg (] ; born 19 January 1966) is a Swedish former world no. 1 professional tennis player (in both singles and doubles). A major proponent of the serve-and-volley style of tennis, he won six Grand Slam singles titles and three Grand Slam men's doubles titles between 1985 and 1996. He also won the Masters Grand Prix and was a part of the Swedish Davis Cup-winning-team four times. In addition he won four Masters Series titles, four Championship Series titles and the unofficial Olympic tournament 1984, was ranked in the singles top 10 for ten successive years, 9 years in the top 5, and is considered one of the greatest players of his era. Edberg began coaching Roger Federer in January 2014, with this partnership ending in December 2015.
Document 8: Boris Becker: Boris Franz Becker (] ; born 22 November 1967) is a German former world No. 1 professional tennis player. He was successful from the start of his career, winning the first of his six major singles titles aged 17. He also won five year-end championships, 13 Masters Series titles, and an Olympic gold medal in doubles. "Tennis" magazine ranked him the 11th best male player of the period 1965–2005.
Document 9: 2004 Australian Open – Men's Singles: Roger Federer defeated Marat Safin 7–6, 6–4, 6–2 in the final to win the Men's Singles title at the 2004 Australian Open tennis tournament. This victory allowed Federer to become world number one the following week for the first time in his career, and he would hold that ranking for a record 237 consecutive weeks.
Document 10: Hicham Arazi: Hicham Arazi (Arabic: هشام أرازي‎ ‎ ; born 19 October 1973) is a former male tennis player from Morocco. He played professionally from 1993 to the end of 2007. The left-hander reached his career-high ATP Tour singles ranking of world No. 22 on November 5, 2001. During his career, Arazi captured one singles title, in Casablanca. "The Moroccan Magician" reached the quarter-finals of the Australian Open twice and the French Open twice. As well as the aforementioned nickname, some tennis analysts called him "The Moroccan McEnroe" due to his talent - he played with incredible touch, and often enjoyed the support of the crowd even when not at home. He led Patrick Rafter, winner of the US Open in 1997 and 1998, two sets to love during the first round of the latter tournament. In the third set he was upset with several line calls, telling umpire Norm Chryst to "get out of here", which sparked the beginning of Arazi's meltdown (and Rafter's comeback). During his career, he notably gained victories over former World No. 1s and Grand Slam champions Roger Federer, Andre Agassi, Yevgeny Kafelnikov, Marat Safin, Lleyton Hewitt, Juan Carlos Ferrero, Carlos Moyá and Jim Courier.
Document 11: Pete Sampras career statistics: This is a list of the main career statistics of American former tennis player Pete Sampras. He turned professional in 1988 and his official retirement occurred in August 2003. During his career Sampras won 64 singles titles, including 14 titles at Grand Slam events. He competed in 16 ties for the United States Davis Cup team between 1991 and 2002 and was a member of the cup winning team in 1992 and 1995. Sampras reached the No. 1 ranking on April 12, 1993 and in total held that position for 286 weeks.
Document 12: 1991 ATP Tour World Championships – Singles: Andre Agassi was the defending champion, but Jim Courier defeated him in the semifinal.
Document 13: 2004 Roger Federer tennis season: Roger Federer won three Grand Slams in 2004 for the first time in his career. The first came at the Australian Open over Marat Safin, 7–6(3), 6–4, 6–2. He went on to win his second Wimbledon crown over Andy Roddick, 4–6, 7–5, 7–6(3), 6–4. In addition, Federer defeated the 2001 US Open Champion Lleyton Hewitt at the US Open for his first US Open title, 6–0, 7–6(3), 6–0. Furthermore, Federer won three ATP Masters 1000 events, one on clay at Hamburg, and two on hard court in Indian Wells and Canada. Federer took the ATP 500 series event at Dubai, and wrapped up the year for the second time over Lleyton Hewitt at the Tennis Masters Cup. Federer was the first player to win three Grand Slams in a single season since Mats Wilander in 1988.
Document 14: 2002 Siebel Open – Singles: The 2002 Siebel Open was an international tennis tournament that took place from February 25 to March 3, 2002. Greg Rusedski was the defending champion but lost in the second round to Todd Martin.
Document 15: 2011 SAP Open – Doubles: Mardy Fish and Sam Querrey were the defending champions, but Fish chose not to compete.Querrey decided to play with Juan Martín del Potro, but lost in the quarterfinals to Mark Knowles and Michal Mertiňák.<br>Scott Lipsky and Rajeev Ram won in the final, 6–4, 4–6, [10–8], against Alejandro Falla and Xavier Malisse.
ground_truth: Andre Agassi