Graf won 22 Grand Slam singles titles, second among male and female players only to Margaret Court's 24. She is the only player to have won all four Grand Slam singles tournaments (Wimbledon, the US Open, the French Open and the Australian Open) at least four times each. In 1988, Graf became the first and only tennis player (male or female) to achieve the Calendar Year Golden Slam by winning all four Grand Slam singles titles and the Olympic gold medal in the same calendar year.
Graf was ranked World No. 1 by the Women's Tennis Association (WTA) for a record 377 total weeks—the longest of any player, male or female, since the WTA and the Association of Tennis Professionals began issuing rankings. She also holds the open era record for finishing as the year-end World No. 1 the most times, having done so on eight occasions. She won 107 singles titles, which ranks her third on the WTA's all-time list after Martina Navratilova (167 titles) and Chris Evert (154 titles).
A notable feature of Graf's game was her versatility across all playing surfaces. She won six French Open singles titles (second to Evert) and seven Wimbledon singles titles (third behind Navratilova and Helen Wills Moody). She is the only singles player to have achieved a Calendar Year Grand Slam while playing on all three major types of tennis courts (grass courts, clay courts and hard courts), as the Calendar Year Grand Slams won by other players before her occurred when the Australian and US Opens were still played on grass. Graf reached thirteen consecutive Grand Slam singles finals, from the 1987 French Open through to the 1990 French Open, winning nine of them. She played in 36 Grand Slam singles tournaments from the 1987 French Open through the 1996 US Open, reaching the finals 29 times and winning 21 titles. She reached a total of 31 Grand Slam singles finals, third overall behind Evert (34 finals) and Navratilova (32 finals).
Graf is considered by some to be the greatest female player. Billie Jean King said in 1999, "Steffi is definitely the greatest women's tennis player of all time." Martina Navratilova has included Graf on her list of great players. In December 1999, Graf was named the greatest female tennis player of the 20th century by a panel of experts assembled by the Associated Press. Tennis writer Steve Flink, in his book The Greatest Tennis Matches of the Twentieth Century, named her as the best female player of the 20th century.
Graf retired in 1999 while she was ranked World No. 3. She married former World No. 1 men's tennis player Andre Agassi in October 2001 and they have two children, Jaden and Jaz Elle.
Steffi was introduced to tennis by her father Peter Graf, a car and insurance salesman and aspiring tennis coach, who taught his three-year-old daughter how to swing a wooden racket in the family's living room. She began practicing on a court at the age of four and played in her first tournament at five. She soon began winning junior tournaments with regularity, and in 1982 she won the European Championships 12s and 18s.
Graf played in her first professional tournament in October 1982 at Stuttgart, Germany. She lost her first round match 6–4, 6–0 to Tracy Austin, a two-time US Open champion and former World No. 1 player. Austin remarked of the then-thirteen year old Graf that "there are hundreds of girls like her in America." (Twelve years later, Graf defeated Austin 6–0, 6–0 during a second round match at the Evert Cup in Indian Wells, California, which was their second and last match against each other.)
At the start of her first full professional year in 1983, the 13-year-old Graf was ranked World No. 124. She won no titles during the next three years, but her ranking climbed steadily to World No. 98 in 1983, World No. 22 in 1984, and World No. 6 in 1985. In 1984, she first gained international attention when she almost upset the tenth seed, Jo Durie of the United Kingdom, in a fourth round Centre Court match at Wimbledon. In August as a 15-year-old (and youngest entrant) representing West Germany, she won the tennis demonstration event at the 1984 Olympic Games in Los Angeles.
Graf's schedule was closely controlled by her father, Peter Graf, who limited her play so that she would not burn out. In 1985, for instance, she played only 10 events leading up to the US Open, whereas another up-and-coming star, Gabriela Sabatini of Argentina, who was a year younger than Graf, played 21. Peter also kept a tight rein on Graf's personal life. Social invitations on the tour were often declined as Graf's focus was kept on practicing and match play. Working with her father and then-coach Pavel Složil, Graf typically practiced for up to four hours a day, often heading straight from airports to practice courts. This narrow focus meant that Graf, already shy and retiring by nature, made few friends on the tour in her early years, but it led to a steady improvement in her play.
1985 and early 1986 saw her emerge as the top challenger to the dominance of Martina Navratilova and Chris Evert. During that period, she lost six times to Evert and three times to Navratilova, all in straight sets. She did not win a tournament but consistently reached tournament finals and semifinals, with the highlight being her semifinal loss to Navratilova at the US Open.
On April 13, 1986, Graf won her first WTA tournament and beat Evert for the first time in the final of the Family Circle Cup in Hilton Head, South Carolina. (She never lost to Evert again, beating her a further seven times over the next three and a half years.) Graf then won her next three tournaments at Amelia Island, Charleston, and Berlin, culminating in a 6–2, 6–3 defeat of Navratilova in the final of the latter. At the French Open, Graf was the third seed but was seen by many as the tournament favorite. However, she caught a virus and lost to Hana Mandlikova in the quarterfinals 2–6, 7–6, 6–1. The illness caused her to miss Wimbledon, and an accident where she broke a toe several weeks later also curtailed her momentum. She returned to win a small tournament at Mahwah just before the US Open where, in one of the most anticipated matches of the year, she encountered Navratilova in a semifinal. The match was played over two days with Navratilova finally winning after saving three match points 6–1, 6–7, 7–6. Graf then won three consecutive indoor titles at Tokyo, Zürich, and Brighton, before once again contending with Navratilova at the season-ending Virginia Slims Championships in New York City. This time, Navratilova beat Graf 7–6, 6–3, 6–2.
Graf won seven singles titles at Wimbledon, six singles titles at the French Open, five singles titles at the US Open, and four singles titles at the Australian Open. Her overall record in 56 Grand Slam events was 282-34 (89 percent) (87-10 at the French Open, 75-8 at Wimbledon, 73-10 at the US Open, and 47-6 at the Australian Open). Her career prize-money earnings totalled US$21,895,277 (a record until Lindsay Davenport surpassed this amount in January 2008). Her singles win-loss record was 900-115 (88.7 percent). She was ranked World No. 1 for 186 consecutive weeks (from August 1987 to March 1991, still the record in the women's game) and a record total 377 weeks overall. Graf also won 11 doubles titles.
In the 1990s, she had a long term relationship with racing car driver Michael Bartels.
She married Andre Agassi on October 22, 2001, with only their mothers as witnesses.  Four days later Steffi gave birth, six weeks prematurely, to their son Jaden Gil. Their daughter, Jaz Elle, was born October 3, 2003.
In 1991, the Steffi Graf Youth Tennis Center in Leipzig was dedicated. She is the founder and chairperson of "Children for Tomorrow", a non-profit foundation for implementing and developing projects to support children who have been traumatized by war or other crises. 
In December 2008, Agassi's childhood friend and former business manager Perry Rogers sued Graf for $50,000 in management fees he claimed that she owed him.
Women Athletes for Tennis