He's signed a contract with Middlesbrough until the end of the 2015/16 season and replaces Tony Mowbray who was sacked recently after a disappointing start to the season.
Karanka worked as Jose Mourinho's assistant at Real Madrid for three years and is, according to Middlesbrough, one of Europe's brightest young coaching talents. "He brings with him some fantastic experience as a player and as a talented young coach. We are all excited about working with him," said Middlesbrough chief executive Neil Bausor.
He left Real Madrid in the summer with the appointment of Carlo Ancelotti and had previously been manager of the Spanish under-16 team.