Answer by taking a quote from the following article:

Stefanie Graf was born on 14 June 1969, in Mannheim, Baden-Wurttemberg, West Germany, to Heidi Schalk and Peter Graf (18 June 1938 - 30 November 2013), a car and insurance salesman. When she was nine years old her family moved to the neighbouring town of Bruhl. She has a younger brother Michael. Graf was introduced to tennis by her father, an aspiring tennis coach, who taught his three-year-old daughter how to swing a wooden racket in the family's living room.

The main weapons in Graf's game were her powerful inside-out forehand drive (which earned her the moniker Fraulein Forehand) and her intricate footwork. She often positioned herself in her backhand corner and although this left her forehand wide open and vulnerable to attack, her court speed meant that only the most accurate shots wide to her forehand caused any trouble. Graf's technique on the forehand was unique and instantly recognizable: generating considerable racquet head speed with her swing, she reached the point of contact late and typically out of the air. As a result, she hit her forehand with exceptional pace and accuracy. According to her coaches Pavel Slozil and Heinz Gunthardt, Graf's superior sense of timing was the key behind the success of her forehand.  Graf also had a powerful backhand drive but over the course of her career tended to use it less frequently, opting more often for an effective backhand slice. Starting in the early 1990s, she used the slice almost exclusively in baseline rallies and mostly limited the topspin backhand to passing shots. Her accuracy with the slice, both cross-court and down the line and her ability to skid the ball and keep it low, enabled her to use it as an offensive weapon to set the ball up for her forehand put-aways. However, Graf admitted in 1995 that she would have preferred having a two-handed backhand in retrospect.  She built her powerful and accurate serve up to 174 km/h (108 mph), making it one of the fastest serves in women's tennis and was a capable volleyer.  An exceptionally versatile competitor, Graf remains the only player, male or female, to have won the calendar-year Grand Slam on three surfaces or to have won each Grand Slam at least four times. Eighteen-time Grand Slam champion and former rival Chris Evert opined, "Steffi Graf is the best all-around player. Martina [Navratilova] won more on fast courts and I won more on slow courts, but Steffi came along and won more titles on both surfaces." Her endurance and superior footwork allowed her to excel on clay courts, where, in addition to six French Open titles, she won 26 regular tour events, including a record eight titles at the German Open. Meanwhile, her naturally aggressive style of play, effective backhand slice and speed around the court made her even more dominant on fast surfaces such as hard courts, grass and carpet. Graf stated that grass was her favorite surface to play on, while clay was her least favorite.

anything else?
Eighteen-time Grand Slam champion and former rival Chris Evert opined, "Steffi Graf is the best all-around player.