Portugal midfielder Bruno Fernandes completed his move from Sporting Lisbon to Manchester United on Thursday, claiming he was inspired to switch to Old Trafford by compatriot Cristiano Ronaldo.
The 25-year-old has signed a five-and-a-half year contract with an option to extend for a further year.
The long-anticipated deal, with an initial fee of 55 million euros (£46 million, $61 million), was finalised after Fernandes, who has 19 international caps, agreed personal terms and passed a medical.
The fee could rise to 80 million euros with add-ons.
Fernandes said he was delighted to be joining the club, who are fifth in the Premier League table.
"My love of Manchester United really started when I used to watch Cristiano Ronaldo play and ever since then I have been a big fan of this great club," Fernandes explained of his Portuguese teammate who played for United from 2003-2009.
"For me, to now play for Manchester United feels incredible.
"I have worked hard to get to this moment and I can promise the fans that I will give everything for the badge to help bring us more success and trophies."
United manager Ole Gunnar Solskjaer admitted Fernandes had been a long-term target.
"We have been tracking Bruno for many months and everyone here has been tremendously impressed with all his attributes and what he will bring to this team," he said.
"Most importantly he is a terrific human being with a great personality and his leadership qualities are clear for all to see.
"Bruno's goals and assists stats speak for themselves. He will be a fantastic addition to our team and he will help us push on in the second part of the season."
United are badly in need of midfield reinforcements due to long-term injuries to Paul Pogba and Scott McTominay, while Marcus Rashford's back problem has also left Solskjaer short of options in attack.
- Goal threat -
Fernandes offers a goal threat, having scored 63 goals in 137 appearances for Sporting since returning to his homeland after spells with Udinese and Sampdoria in Italy.
There had been mounting pressure on United's executive vice-chairman Ed Woodward to land at least one marquee name during the January transfer window.
Woodward, who has overseen the club's poor recruitment over the past seven years, had been the target of the fans' anger in a 2-0 home defeat by Burnley last week.
United are an incredible 36 points behind runaway leaders Liverpool and six points adrift of the Champions League places.
Their chances of a top-four finish will depend greatly on how they fare in their next two league games at home to Wolves on Saturday and then away to fourth-placed Chelsea on February 17.
The Europa League offers another potential route into next season's Champions League and Fernandes will be eligible to feature for United when that competition returns next month, despite already playing for Sporting in the group stages.