Qatar emir's sister Sheikha al-Mayassa is art world's most powerful figure

Her full title is Her Excellency Sheikha al-Mayassa bint Hamad bin Khalifa al-Thani, and although the 30-year-old is a long way from being a household name, she is the most powerful person in the art world.

The sheikha, daughter of the former emir of Qatar and sister of the current one, heads the Qatar Museums Authority. As such, she has control of the biggest cash pile in the world when it comes to buying Western modern and contemporary art. Her family is thought to spend more than US$1 billion a year on works for the museums Qatar is creating from scratch in the desert.

Sheikha Mayassa tops a list now in its 12th year: the ArtReview Power 100, a ranking of how the dealers, collectors, curators and artists compare in their importance to the delicate ecosystem of contemporary art.

"I think the figures definitely speak for themselves, and of the importance she has for the art market," said Mark Rappolt, ArtReview's editor.

The Museums Authority is thought to have been behind the record US$250 million purchase of a Cezanne painting of two card players. The 2011 sale, details of which have never been officially confirmed, was about double the previous record for a painting.

The purchase instantly put the Museums Authority into the big leagues of international collections, with the others in Cezanne's five-painting series held by the Musee d'Orsay in Paris, the Metropolitan Museum of Art in New York, the Courtauld Institute of Art in London and the Barnes Foundation in Philadelphia.