An Oxford and Harvard trained economist, Ed Balls has been described as 'Gordon Brown's other brain'.
Now in the cabinet, he has been charged with implementing education policy, which the new prime minister has called as his "passion".
He worked for the then shadow chancellor in opposition - furnishing his intellectual reputation with the phrase "post-neoclassical endogenous growth theory" - and later in office, where the two were said to have developed Britain's five tests for joining the euro while sitting in the back of a New York taxi.
The former Financial Times journalist also briefs the media on behalf of Brown, on and off-the-record.
As his right-hand man for most of his 10 years at the Treasury, Balls, 39, was one of the favourites to become Brown's first chancellor.
Although he may have to wait a little longer to take that job, he has been trusted to run a big spending department and a key economic role in the new government as secretary of state for children, schools and families.
Once described as the most powerful unelected person in Britain, Balls gave up his position as Brown's chief adviser to become a backbench MP for Normanton, the neighbouring seat to that of his wife Yvette Cooper who now joins him in attending the cabinet.
Within a year of his election he was officially back in Brown's team, promoted to the government as economic secretary of the Treasury in the reshuffle of May 2006.
There he has helped court the City as well as serve on the small team preparing Brown's strategy for government.
