Here we recall some of his memorable comments from his time in charge at Old Trafford.
"Yes, I think (we can). What gives me that belief? It gives me the belief that we are going to make much more points in the second part of the season than we did in the first part. I know we lost some other matches but we played away at Liverpool, Chelsea and Manchester City - probably the three best teams apart from Tottenham" - Mourinho insists United can finish the season in the top four, despite a 3-1 defeat at Liverpool which left them in sixth place and 11 points off fourth-placed Chelsea on December 16, 2018.
"Let me send a message to my lovers and say that I played Champions League for 14 years and I qualified 14 times. And the two years where I didn't play Champions League, I won the Europa League twice, so in 16 years, 14 times I qualify and twice I play Europa League and I won. Just a little curiosity for my lovers and the lovers of the stats" - November 27, 2018, after qualifying for the Champions League knockout stages following Marouane Fellani's last-gasp winner at home to Young Boys.
"I know it's a big gap but I also know, until the end of December, if I'm not wrong, we have eight Premier League matches to play, and eight Premier League matches, we are speaking about 24 points. Twenty-four points for us to fight (for), 24 points for the other ones that are in the top four to fight (for) too, but I believe we are going to be there" - Mourinho believed the Red Devils would be inside the Premier League's top four by the end of 2018 on November 23, 2018.
"Do you know what was the result? Three-nil. Do you know what this means (holding up three fingers)? Three-nil but it also means three Premier Leagues and I won more alone than the other 19 managers together. Three for me and two for them. Respect, respect, respect" - leaving the post-match media conference angry at a perceived lack of respect following the August 27, 2018, 3-0 Premier League loss to Tottenham at Old Trafford.
"You can be a rich club and buy all the best players in the world but you cannot buy class...because I am in the movie I could ask for some royalties" - criticising neighbours Manchester City for their Amazon Prime documentary on August 18, 2018.
"One lie repeated 1,000 times is still a lie, but the perception of the people is that it's true but it's still a lie. So, when you repeat 1,000 times that my relationship with my players is not good, it's a lie that repeated 1,000 times is still a lie" - on August 9, 2018, after the summer transfer window closed without United adding the centre-back he craved.
"I wouldn't spend my money to see these teams" - after a weakened United lost 4-1 to a Liverpool side without their leading players in Michigan in the International Champions Cup on July 28, 2018.
"I don't answer to your question" - refusing to be drawn on whether United can challenge for the Premier League title on July 27, 2018.
"When you start the process, you are here, you are there, or you are there. It is heritage. It's heritage" - part of a lengthy rant, using prepared notes, on March 16, 2018, in defence of United's Champions League exit to Sevilla a few days earlier.
"That's not the end of the world. I sit in this chair twice in the Champions League and I knock out Man United at home at Old Trafford. I sit in this chair with Porto, Man United out. I sit in the chair with Real Madrid, Man United out. So, I don't think it is something new for the club and of course being Manchester United manager and losing a Champions League tie at home is a disappointment" - in the immediate aftermath of the Champions League last-16 exit to Sevilla on March 13, 2018, Mourinho makes bizarre reference to eliminating United when he was an opposition manager.
"We have set very high standards - winning three trophies in one season - but those are the standards I expect my teams to aim for" - after signing a new contract until 2020, on January 25, 2018.
"What never happened to me and will never happen to me is to be suspended for match-fixing" - a war of words with Antonio Conte escalated in January 2018 when the Portuguese made reference to the Italian's four-month ban for failing to report attempted match fixing, which was later overturned and saw Conte acquitted.
"If you ask me one thing that I don't like a lot it's that they lose their balance very easily. You know, a little bit of wind and they fall" - accuses Manchester City of simulation on December 9, 2017, ahead of the Manchester derby.
"The local injections before the match, we were not informed (about)" - takes a swipe at England after claiming United were not informed about Phil Jones' pain-killing injections for a thigh problem on November 21, 2017.
"I think a quarter of the planet is Manchester United red. I cannot meet them" - after declining an invitation to meet fans' representatives to discuss tensions between himself and supporters on November 3, 2017.
"The only thing I can say is that I'm still a coach with worries, with ambitions, and with the desire to do new things. And I don't believe... no, I'm sure that I won't end my career here" - says United will not be his final job in an October 15, 2017, interview with a French broadcaster, in comments interpreted as a flirtation with Paris St Germain.
"There was an evolution in the other clubs; there was no evolution in this club. In all the areas that make a team successful I think we stopped in time. That was quite an empty period in the club" - Mourinho on September 10, 2017, appraising the spells of predecessors David Moyes and Louis van Gaal.
"I'm not going to lose my hair to speak about Antonio Conte" - makes a reference to then Chelsea boss Conte's hair transplant on United's pre-season tour in July 2017.
"If we could, we would change obviously the people's lives for this cup - immediately, we wouldn't think twice. Does this cup make the city of Manchester a bit happier? Maybe" - after the Europa League final defeat of Ajax on May 24, 2017, which came fewer than 48 hours after 22 people were killed and many more injured in the Manchester Arena bombing.
"I see a difference between matches. I don't think it's consistent, the atmosphere and enthusiasm" - questioning the atmosphere at Old Trafford on May 10, 2017, ahead of the Europa League semi-final with Celta Vigo.
"He was in front of me and I was making every decision for him. He has to change his football brain. We need his fantastic physical and technical qualities but he cannot play with my brain" - after a 1-1 draw with Everton in April 2017, Luke Shaw is told to "grow up" quickly.
"Manchester United sold players that I would never sell and bought players that I would never buy. I would never have sold Di Maria, Chicharito, Danny Welbeck - never, no chance" - questions United's transfer policy on March 16, 2017.
"The player asked for a banana and it is not to laugh at all, it is to respect the players and their limits. They gave absolutely everything" - after Marcos Rojo asked for a banana during the Europa League win over Rostov on March 16, 2017.
"They can call me what they want. Until the moment they have a manager that wins four Premier Leagues for them, I'm the number one. When they have somebody that wins four Premier Leagues for them, I become number two. Until this moment Judas is number one" - Mourinho responds to Chelsea supporters labelling him 'Judas' during United's 1-0 FA Cup quarter-final loss at Stamford Bridge on March 13, 2017.
"I put a lot of pressure on myself; you put a lot of pressure on myself. I wanted very much to win a major trophy at every club; by doing that with Manchester United it's quite the sense of relief because it was a big target for me" - after defeating Southampton in the February 26, 2017, League Cup final to win his first trophy as United boss.
"It is my little homage to somebody that wrote the most beautiful history of the Premier League. Somebody that probably would deserve the Leicester stadium to be named 'Claudio Ranieri' - and he is sacked" - after attending his weekly media conference in a shirt emblazoned with the initials 'CR' to show solidarity with Claudio Ranieri, the title-winning boss sacked by Leicester, in February 2017.
"You do your job and you do a public service, I think. Tell the truth. It's as simple as that. I am different in everything: I watch my team play in a hotel, I was forbidden to go to the stadium, my assistant had a six-match stadium ban and he didn't touch anyone" - rounds on the media and disciplinary officials after the February 1, 2017, goalless draw with Hull.
"There is a difference between the brave, who want to be there at any cost, and the ones for whom a little pain can make a difference" - appears on November 7, 2016, to cast doubt on Chris Smalling and Shaw's claims they are injured after the defensive pair missed a win at Swansea.
"If, at the end of the three years, I don't win a single piece of silverware for them, they will say 'great guy, good coach, we like him, but we feel nothing special about him'" - acknowledging on October 22, 2016, he must win to be 'special' to United fans.
"We had a bad week. I know that some football Einsteins, they tried to delete 16 years of my career and delete an unbelievable history of Manchester United Football Club and focus on a bad week and three bad results. But that's the new football - it's full of Einsteins" - after successive losses to Manchester City, Feyenoord and Watford, on September 22, 2016.
"We feel that we are candidates to win the title" - in optimistic mood on August 12, 2016.
"Maybe he (Wayne Rooney) is not a striker, not a number nine any more but for me he will never be a number six, playing 50 metres from the goal" - on Wayne Rooney, on July 5, 2016.
"It is a job every one wants and not many have a chance to have and I have it" - at his unveiling on July 5, 2016.