Manchester United have completed the signing of striker Romelu Lukaku from Everton for a reported initial fee of £75million.
The 24-year-old passed a medical in Los Angeles at the weekend shortly after United announced that they had reached an agreement with Everton over the transfer.
The Belgium international has signed a five-year deal, with the option of an additional year, to become Jose Mourinho's second signing of the transfer window, following the arrival of defender Victor Lindelof from Benfica.
"I would like to start by thanking Everton and the fans for the last four wonderful seasons, I have made some special friends and we have shared some amazing moments," Lukaku said after his move was finalised on Monday.
"However, when Manchester United and Jose Mourinho come knocking at the door it is an opportunity of a lifetime and one that I could not turn down.
"You could see the fight, determination and the spirit in this team during the Europa League final and I want to become a part of that.
"I cannot wait to run out at Old Trafford in front of 75,000 fans but before that pre-season is where the hard work starts and I am looking forward to that first training session."
Lukaku's switch comes after Wayne Rooney moved in the opposite direction, completing a move back to his boyhood club Everton on Sunday.
Mourinho believes Lukaku, who he previously managed at Chelsea, is ideally suited to United.
"Romelu is a natural fit for Manchester United," said Mourinho. "He is a big personality and a big player.
"It is only natural that he wants to develop his career at the biggest club. He will be a great addition to the group and I know they will make him very welcome. I am really looking forward to working with him again."
Lukaku scored 25 goals in the Premier League last season to help Everton to a seventh-place finish and a spot in the Europa League.
He agreed to move to Old Trafford despite a reported attempt from former club Chelsea to hijack the deal at the last minute.
The powerful forward has been signed as a replacement for Zlatan Ibrahimovic, who was released at the end of his contract after suffering a serious knee injury in April.
Lukaku is the second-most expensive signing in United's history, behind only Paul Pogba, who joined from Juventus last year for a world-record £89.3m.