The 40-year-old Spaniard turned down top-flight strugglers Crystal Palace to move to Teesside after taking advice from Chelsea boss Mourinho, with whom he worked for three years as an assistant at Real Madrid before the pair left last summer.
And Karanka is convinced he has joined a club capable of arresting a slide which has seen them slip to within five points of the Skybet Championship relegation zone and accounted for his predecessor Tony Mowbray last month.
Karanka said: "The expectation of the Middlesbrough supporters is to be in the Premier League and I am going to work hard every day to achieve this dream.
"This is the best option for me. I know the history of this club because I was close to signing as a player in 2005. I would have loved to play here but it was not possible, but now I have the chance to start here and it is unbelievable for me."
Karanka had also been favourite to take over at Palace and although he would not comment on the extent of his negotiations with the Eagles, the shiny credentials of a man who worked so closely with Mourinho clearly represent something of a coup.
Mourinho said earlier this month that any English club would be "lucky" if they got Karanka, who made 93 appearances as a defender for Real Madrid before moving into coaching with the Spanish under-16 team in 1993.
And Karanka clearly took heed of Mourinho's advice as he contemplated the options for his first solo role in club management, preferring a club with world-class training facilities and a reputation for bringing young players through its Academy.
Karanka said: "I have been three years with Jose Mourinho and he was supporting me every day. I learned from him and his staff and I think I am ready to start.
"You can learn everything from him on the pitch and off the pitch and in the training room, he's great - he's the one.
"He's a person who was supporting me. I was speaking with him and he recommended to me that I should come here because he believes in this project like me."
Boro chairman Steve Gibson is convinced he has got the right man to lead the club back into the top flight after Gareth Southgate, Gordon Strachan and Tony Mowbray all failed to arrest the slide which started with the departure of Steve McClaren in 2006.
Karanka is Boro's first ever foreign coach, but Gibson insisted his appointment was down less to his nationality and more to his desire to cast the net far and wide in his search for the best possible candidate for the post.
Gibson revealed the club had 100 applications and added: "We set down a clear template of what we were looking for and Aitor met the criteria we were looking for. He was the outstanding candidate.
"We needed to freshen up our thinking because the game has changed so quickly in the last five or six years. It was time for change but not just for the sake of change, because it was right to change, and we're convinced of that.
"Aitor is probably the most decorated player we have ever had at this club, he has had a very distinguished career and you don't get to become coach of a Spanish national team and Jose Mourinho would not pick you unless you had something.
"We've had many discussions and his footballing philosophy excites everybody he speaks to. But these are just words. What we need now is a passage of time to get this club back into the Premier League, and it will take a lot of hard work and a lot of changes."
Gibson refused to comment on the fate of the club's backroom staff including Mark Venus who took charge on an interim basis following Mowbray's departure. Karanka's first game will be at Leeds a week on Saturday.
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- Tony Mowbray
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