Robert Lustig is a pediatric endocrinologist at the University of California, San Francisco. He is the author of Fat Chance: Beating the Odds against Sugar, Processed Food, Obesity, and Disease. He specializes in childhood obesity and studying the effects of sugar in the diet. He is the director of the UCSF Weight Assessment for Teen and Child Health Program and a member of the Obesity Task Force of the Endocrine Society.
Unfortunately, much of what he says is simply wrong, which given the amount of media exposure that he receives, is deeply worrying.