The Portuguese arrived back at Stamford Bridge in 2013 and guided the club to third in his first season back, famously derailing Liverpool's title bid in the process.
Then in 2014/15, Mourinho's Blues dominated the division and stormed to the Premier League title.
But in 2015/16, everything went pear-shaped, with Mourinho infamously clashing with physio Eva Carneiro on the opening day of the season and falling out with a number of players
Results took a sour turn and Chelsea sacked Mourinho in December.
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Eventful, to say the least and during that two-and-a-half year spell, Mourinho made 28 signings for Chelsea.
So what happened to all of them? Well don't worry, we've got you covered!
One of the few still at the club. The Brazilian was stolen from under the noses of Tottenham and he's gone on to enjoy a mixed career with the Blues.
Some days he looks like a world beater, others a hinderance to the team. Nevertheless, Chelsea managers seem to value him highly.
The lynchpin in Mourinho's midfield, one so important the the Portuguese signed him for Manchester United in 2017.
Matic is still at Old Trafford, but a January exit is firmly on the cards.
So much promise, but just not enough consistency.
Schurrle showed glimpses of his quality in London, but it was never enough to earn him a regular spot. He's now on loan at Spartak Moscow from Borussia Dortmund.
What ever happened to him? Well, following his dismal spell with Chelsea, Salah decided to rebuild his reputation in Italy with Fiorentina and Roma.
Then in 2017, Liverpool brought him back to England and he has become one of the world's finest players. If only Mourinho had given him more of a chance...
The French centre-back is finally getting game time at the Blues after David Luiz's summer exit.
His loan spell at Everton appears to have done him the world of good and he could be a Chelsea mainstay for years to come.
Marco van Ginkel
Few players in the history of football have been as unlucky with injuries as Van Ginkel.
The Dutchman is still at the club and is currently on the sidelines with another serious knee injury, one he picked up just as he was thriving on loan at PSV Eindhoven.
One of the former members of Chelsea's 'loan army'.
Temporary stints at Vitesse, Everton, Bournemouth, Malaga and Newcastle weren't enough to earn him a spot in the Blues' first-team and he's now with the Toon Army on a permanent basis.
The 24-year-old Croatian striker failed to make a senior appearance for Chelsea, resulting in a move to Udinese in 2015.
Perica is now on loan at Belgian side Royal Excel Mouscron, where he is still waiting to make his debut for the club.
Four years with the Blues, no senior appearances and loaned out four times; sound familiar?
Like many Chelsea signings down the years, Cuevas never got his chance and he was sold to Chilean side Huachipato in 2017. He's currently on loan at Austria Wien.
An inspired free transfer.
Eto'o scored some crucial goals during his season with the Blues, before signing for Everton in 2014. Following a short spell with Qatar SC, the Cameroonian announced his retirement this year.
Signed purely as a back-up goalkeeper, Schwarzer made just four appearances during his two years in west London.
After spending 2015/16 with Leicester, the Australian called time on his long, illustrious career.
Until Tammy Abraham's arrival into the first-team this season, Costa's exit in 2017 at the wishes of Antonio Conte just looked bizarre.
The Spaniard was Mourinho's go-to man, scoring goal after goal. He's now back at Atletico Madrid were finding the back of the net has got a lot tougher for him.
A signing which helped deliver Mourinho another Premier League title.
Fabregas' arrival in 2014/15 changed the Blues' midfield and his partnership with Costa provided so many goals. He's now at Monaco after leaving Chelsea in January.
It's easy to forget the Colombian played for Chelsea, but he arrived at Stamford Bridge in the 2015 January window
However, after making just 13 appearances in the final half of the 2014/15 season, he was loaned out to Juventus where he remains on a permanent basis to this day.
The Brazilian followed Costa to Chelsea from Atletico in the summer of 2014, but endured a different experience to the Spaniard.
After failing to break into the first-team, Luis re-joined Atletico in 2015, before finally leaving Diego Simeone's side this summer for Flamengo.
A dependable back-up, but he was never going to be a regular at Chelsea.
After spells with Crystal Palace, Getafe and Las Palmas, Remy is back in France with Lille where he's finding game time far easier to come by.
Amazingly, Pasalic - who is only 24 - is still a Chelsea player, despite making a grand total of zero appearances in his five years on the club's books.
He's been loaned to Elche, Monaco, AC Milan and Spartak Moscow, before finding himself at Atalanta on a temporary basis for 2019/20.
The club legend was brought in to play backup to Costa and he performed the task admirably.
Drogba left for Montreal Impact in 2015 and he announced his retirement in November 2018 following a goal-filled season with Phoenix Rising.
2015/16 (Matt Miazga and Alexandre Pato were signed after Mourinho was sacked):
While he's never replicated the form he showed at Barcelona for the Blues, Pedro has still been a decent signing.
He's scored crucial goals under Mourinho, Conte and Maurizio Sarri, but he's going to struggle to break into Frank Lampard's current side.
The Ghanian arrived with a glowing reputation, but opportunities at Chelsea are never easy to come by.
Two separate loans at Schalke and one at Reims have not seen him enter the Blues' first-team plans and Rahman is now with Real Mallorca for the 2019/20 season.
Another back-up goalkeeper and another that barely featured for Chelsea, mainly due to Thibaut Courtois' brilliance.
Begovic signed for Bournemouth in 2017 but after falling out of favour with the Cherries, he was loaned out to Qarabag this summer.
Unsurprisingly, Kenedy's Chelsea career has been spent packing his bags and departing the club on loan.
Spells with Watford and Newcastle (twice) did little to enhance his reputation at the Blues, so they shipped him out to Getafe for the 2019/20 campaign.
Despite his struggles with United, Falcao decided to give English football another shot with Chelsea.
Once again it didn't work out, but he returned to Monaco and remastered the art of goal scoring, before sealing a move to Galatasaray this summer.
The English centre-back was loaned out 11 TIMES by Reading before Chelsea snapped him up in 2015.
Since then, you guessed it, the Blues have also loaned him out another four times, the most recent being Sheffield Wednesday in 2018/19. This season, he's remained at Chelsea, but he's yet to make an appearance.
No we haven't missed out a second name here, Nathan is a Brazilian attacking midfielder who is a firm member of the Chelsea loan army.
Vitesse, Amiens, Amiens II and Belenenses all took a gamble on the 23-year-old, but he's now on loan at Atletico Mineiro where he has been since July 2018.
Djilobodji famously made one appearance for the Blues, coming on in injury-time during a League Cup clash versus Walsall.
The Senegalese then joined Sunderland in 2016, but after failing to make an impact in the north of England, the centre-back decided to look elsewhere. He's now at Turkish side Gazisehir Gaziantep.
Pantic arrived from Partizan Belgrade in 2015 and returned to the club in 2017 on a two-year loan.
The 22-year-old Serbian is still a Chelsea player and he is currently on loan at Hungarian side Fehervar.
Amelia arrived at Stamford Bridge near the end of his career, spending just one season with the Blues before a move to Vicenza.
He retired back in 2017 and is now the head coach of Serie D club, Vastese.News Now - Sport News