It's the biggest company you've never heard of. Glencore - a commodity giant that trades huge quantities of wheat, coal and much of the world's copper. John Sweeney talks exclusively to its boss, Ivan Glasenberg, who became a billionaire five times o... (more)ver when the company was listed on the London stock exchange last year. But, in Congo and Colombia, Glencore stands accused of reckless greed. Panorama investigates.