She's snubbed him because leaked documents suggest the NSA has been spying on her and the Brazilian oil and gas firm Petrobras

Age: 65.

Appearance: Jack Black: The Powerful Woman Years.

Who is she? The second-most powerful woman in the world.

Says who? And why? Says Forbes magazine. Because she's the president of Brazil.

And what has she done now? Snubbed the world's most powerful man. Rousseff has postponed an official visit to Washington to meet with Barack Obama.

On what grounds? On the grounds that there has yet to be "a timely investigation" into reports, based on documents leaked by Edward Snowden, that the US National Security Agency has been spying on her phone calls and emails, her aides and the state-controlled oil and gas firm Petrobras.

And this is a problem for her? Yes. Quite a big problem.

Why? Apart from the fact that, as a rule, people don't like being spied on? Because Rousseff is quite protective when it comes to Petrobras. As are the people of Brazil. The government-run firm is the country's largest company and produces more than 90% of Brazil's oil and natural gas. Plus Rousseff was chair of its board of directors for seven years. Making it kind of her giant multibillion dollar baby.

So she's an oil baron who went into politics? No, if anything she's a radical politician who went into oil. Rousseff's political life began on the far left, in the underground resistance to the military dictatorship that seized power in Brazil in 1964. She was arrested in 1970 and tortured with electric shocks to her feet and ears, before spending the next three years in prison.

How did she get from there to president? With a steely determination for which she was dubbed Brazil's "Iron Lady". She entered the government as energy minister, rose through the ranks, and ran for president after an extensive makeover – including heavy dental work and plastic surgery – to make her look softer and more electable.

But she's still as hard as nails? Clearly. And, after snubbing the US president, just a little bit more re-electable.

Do say: "The lady's not for alleged industrial espionage."

Don't say: "What, we can't spy on your state-run oil firm now? Come on!"