The former Real Madrid assistant coach replaces Tony Mowbray as the Championship side's manager, having agreed a two-and-a-half year contract at the Riverside StadiumMiddlesbrough have appointed Aitor Karanka as their new manager.
The former Real Madrid assistant coach will begin work at the Riverside Stadium immediately after agreeing a two-and-a-half year deal at the club.
Karanka, who was Jose Mourinho's right-hand man in Spain, is Middlesbrough's first ever foreign coach and is excited to be working at a club recommended to him by the Portuguese.
"It's a very important day for me - it's my new job," he enthused to reporters.
"I think it's the best thing in the world because I find a club like a family, with a big stadium, big supporters.
"It's my time. I have worked with Jose Mourinho and he was a great influence, I learned a lot from him. He's a person who has helped me for months I always speak with him and he told me to come here."
Middlesbrough's chief executive, Neil Bausor, told the club's official website: "We are delighted that Aitor has decided to further his coaching career with Middlesbrough as our head coach.
"He brings with him some fantastic experience as a player and as a talented young coach. We are all excited about working with him."
Karanka played for Athletic Bilbao, Real Madrid and Colorado Rapids in a career spanning 15 years before becoming Madrid's assistant in 2010.