Christy Walton, 56, is the widow of John T Walton, one of the sons of Walmart founder Sam Walton.

She inherited John's fortune of $15.7 million when he died in June 2005 and now has an estimated net worth of about $25 billion, making her the tenth richest person in the world.

Liliane Bettencourt, 88, is France's richest woman with an estimated fortune of $23.5 billion.

Her wealth is due to being heir to the French cosmetics giant L'Oreal, which was founded by her father.

While Christy Walton's wealth is thanks to her marriage to John T Walton, Alice, 61, inherited her fortune directly from her father, Sam.

He founded Walmart, which now employs some 2.1 million people, in 1962 with his brother James. Alice's personal wealth is estimated at $20.9 billion.

When billionaire Andronico Luksic died of cancer in 2005, his second wife Iris became head of the family that controls Antofagasta, one of the world's largest copper miners.

Her fortune is thought to be worth about $19.2 billion.

Susanne Klatten, 48, is the daughter of Herbert Quandt, the man who rescued BMW from bankruptcy in the 1960s.

She also owns chemical manufacturer Altana, which she delisted from the stock market after inheriting 50% and increasing her stake to 100%. Her wealth is estimated at $14.6 billion.