Venus Williams and Serena
Venus Ebony Starr Williams - four-time winner of Wimbledon, double US Open champion, and at one point, world number one - is regarded by many as the most dominant player in women's tennis. Throughout her career, however, sister Selena has constantly challenged her position as the queen of the court.
Born on June 17, 1980, and September 26, 1981, the youngest of five sisters, Venus and Serena were not much more than toddlers when their father, entrepreneur Richard Williams, set in motion what was to become a sporting juggernaut. Legend has it that before the two girls were born, their father, having watched Virginia Ruzici pick up $22,000 for winning the French Open women's singles championship, vowed that any future children he might have with wife Oracene would be tennis players.
He started teaching a four-year-old Venus on a court in Los Angeles' notoriously rough East Compton park, but in 1988, disgusted by the behaviour of fanatical parents on the junior tennis circuit, tried to persuade his eight-year-old daughter to quit. She refused, and a year later, gave up a promising track career - despite having clocked up an incredible 5.29-minute mile the previous year - in order to concentrate on her tennis.
In 1991 Richard uprooted his family to enrol both Venus and Serena in Rick Macci's Delray Beach Tennis Academy in Florida, where they trained, "six hours a day, six days a week for four years".
This dedication paid off when the sisters turned professional. Each landed a $12-million sponsorship deal while still in their early teens - Serena's deal with Puma being dependent on her entering the world's top ten players. And to this day it remains difficult to separate the siblings' achievements.
Both divide their time between their tennis commitments and various off-court interests, including fashion design.
Competitiveness has brought the sisters together rather than driving them apart, however. Close friends, they reportedly stay in contact by e-mail between matches and enjoy each other's company when appearing at the same event. When Venus won her first Wimbledon grand slam in 2000 against Lindsay Davenport, the sisters sat up until 2am celebrating - then went on to win the women's doubles the next day.
But this very closeness has also contributed to allegations of match fixing against their high-profile, image-conscious father, who has been accused of orchestrating his daughters' careers to maximise their collective financial potential and titles.
Venus took the Wimbledon title for the second time in 2001 and the same season returned to defend her US Open title in a historic sibling showdown. That time Venus prevailed, but it was a bitter-sweet moment. "I don't exactly feel like I've won," Venus said afterward. "I just hate to see Serena lose, even against me. I'm the big sister. I make sure she has everything, even if I don't have anything. I love her and it's hard."
By 2002 Serena's game had improved considerably and she won eight tournaments, including the coveted Wimbledon title. By July she had secured the number one ranking, knocking sister Venus off the spot.
Venus regained her form, however, securing her third Wimbledon title in 2005, and her fourth two years later, saying that she had been inspired to win by her sister. In 2008 she again became the top ranked US woman, a position she last held in May 2002 when she was also world number one.