Jose Mourinho says no other club in world football is capable of matching the "mystique and romance" of Manchester United.
The Portuguese manager was officially confirmed as the club's new boss on Friday after a week of negotiations following Louis van Gaal's sacking on Monday.
Mourinho has penned a three-year contract at Old Trafford with an option of an extra year to keep him at the club until 2020.
"To become Manchester United manager is a special honour in the game," Mourinho said.
"It is a club known and admired throughout the world. There is a mystique and a romance about it which no other club can match.
"I have always felt an affinity with Old Trafford; it has hosted some important memories for me in my career and I have always enjoyed a rapport with the United fans.
"I’m looking forward to being their manager and enjoying their magnificent support in the coming years."
United's executive vice-chairman Ed Woodward added: "Jose is quite simply the best manager in the game today.
"He has won trophies and inspired players in countries across Europe and, of course, he knows the Premier League very well, having won three titles here.
"I’d like to take this opportunity to welcome him to Manchester United. His track record of success is ideal to take the club forward."