Mark Coles profiles Robert Mueller who's just been appointed as special counsel to oversee the investigation into Russian interference in the US election. Mueller retired as director of the FBI four years ago, but now finds himself centre stage again.

The squared-jawed Princeton graduate was decorated for bravery during the Vietnam War before training as a lawyer. Dissatisfied with private practice, he found a government job as assistant US attorney in San Francisco - a move which marked the beginning of a steady climb to the top of law enforcement in America.

Robert Mueller became FBI director one week before the 2001 World Trade Center attacks and over the next twelve years transformed the organisation, moving thousands of staff from criminal investigations into counter terrorism and security. Yet surprisingly little is known about him personally.