Roman Abramovich walked into Stamford Bridge in the summer of 2003 and wasted little time in transforming world football as we knew it.
The Chelsea owner would splash the cash left, right and centre with the sole goal of turning the Blues into a European superpower, and with his era at the club coming to a close, it's safe to say that he managed that.
Helping him on the way were a number of outstanding signings, and here are 15 of the best.
1. Claude Makelele
Makelele left Real Madrid in 2003 amid claims from Blancos chiefs that he was washed up and ineffective. Throughout his five years at Chelsea, he laughed in the face of those critics.
Widely heralded as one of the best defensive midfielders in Premier League history, Makelele redefined his own role and is still the gold standard against which any new players are held.
He won two league titles in England before leaving on a free transfer for PSG in 2008.
2. Joe Cole
When West Ham were relegated to the second tier in 2003, Cole was one of a handful of players who jumped ship. The 21-year-old was Chelsea's sixth signing of the Abramovich era, and you'll struggle to find too many that were better than him.
A versatile midfielder, Cole was never a superstar player for Chelsea but he offered seven years of great sidekick service, playing among a whole host of huge names and always holding his own.
He got his hands on three league titles and was named in the PFA Team of the Year in 2005/06.
3. Didier Drogba
Of the ten most-important goals in Chelsea's history, Drogba was probably responsible for eight or nine of them. The legendary striker showed up on the biggest stages and wrote his name into folklore with some huge goals.
The most famous of his 164 goals for the club came in the 2012 Champions League final, in which he dragged Chelsea to glory over Bayern Munich by netting an equaliser and then the winning penalty.
Drogba is a Chelsea legend, a Premier League icon and an African superhero. It's safe to say this deal worked out pretty well.
4. Ricardo Carvalho
Carvalho's time at Chelsea wasn't always easy, but when he was firing on all cylinders, there was nobody on the planet who could touch him.
After following Jose Mourinho from Porto in 2004, Carvalho formed an iconic centre-back partnership with John Terry that conceded just 15 goals in 38 league games. That's still a record and the idea of somebody breaking it is incomprehensible.
Never the most athletic defender, Carvalho's unparalleled intelligence on the pitch still sees him sit towards the top of Chelsea's all-time greatest defenders.
5. Petr Cech
The debate for the Premier League's best goalkeeper has just two answers: Peter Schmeichel or Petr Cech.
Plucked from relative obscurity in 2004, Cech immediately became Chelsea's starting goalkeeper and kick-started a decade of overwhelming success, lifting four Premier League titles and the 2011/12 Champions League.
His list of personal records is enormous. Among them are: most Premier League clean sheets (202), most clean sheets in a season (24 in 2004/05), fastest goalkeeper to both 50 and 100 clean sheets and most appearances in major cup finals for Chelsea (14).
6. Michael Ballack
Chelsea don't exactly have a rich history of free transfers, but they do have some of the greatest Bosman deals in history. Towards the top of that list is Ballack.
The 29-year-old chose Chelsea over Manchester United, which already made him a hero, and his performances on the pitch only added to his legacy.
Of his 105 Premier League appearances, Ballack lost just ten games. He won the 2009/10 title and picked up three FA Cups for good measure.
7. Ashley Cole
Fee: £5m plus William Gallas
Potentially the best English left-back ever, Cole joined Chelsea in 2006 for what feels like pocket change.
Already a star from his time with Arsenal, Cole continued to boost his stock on the blue side of London, getting his hands on one Premier League title, a Champions League winner's medal and no fewer than four FA cups.
Cole enjoyed eight years at Stamford Bridge, and since his departure in 2014, the Blues have had a torrid time trying to replace him.
8. Branislav Ivanovic
Another player plucked from relative obscurity, Ivanovic swapped Lokomotiv Moscow for Chelsea in January 2008 but looked to be a disaster of a signing, failing to appear in his first six months due to a lack of fitness and underwhelming training performances.
Exit rumours were huge but Ivanovic stayed strong and he eventually turned things around, emerging as an elite right-back with a dominant eye for goal.
Of his 261 Premier League appearances for Chelsea, 240 of them came as a starter - something very few saw coming in 2008.
9. Gary Cahill
Brought in from bottom-of-the-league Bolton midway through the 2011/12 season, Cahill had to convince fans that his former side's struggles were not his fault, and he managed exactly that.
He formed a superb defensive partnership with John Terry and wasted little time in racking up the silverware. He won every trophy available to him apart from the Club World Cup, but fans will still happily sing about how he's 'won it all'.
Cahill took the captain's armband in the immediate aftermath of Terry's departure and served with real class. His departure in 2019 was a little ugly through no fault of his own but fans have not let that tarnish his legend.
10. Juan Mata
Mata's Chelsea career lasted just two-and-a-half years and was brought to an abrupt end by Mourinho, who was seemingly not impressed with the outrageous level - two club Player of the Year awards on the bounce - that the Spaniard had managed.
His 2012/13 season, which yielded 19 goals and 35 assists in 64 appearances, may well be one of the greatest individual campaigns we have ever seen from a Chelsea player and would have easily led to Mata becoming a club icon if he hadn't fallen foul of Mourinho.
The boss sold him to Manchester United for £37.1m in January 2014, meaning Mata actually brought Chelsea a profit when all was said and done.
11. Cesar Azpilicueta
Appearances: 461 (ongoing)
Truthfully, very few Chelsea fans cared when Azpilicueta was signed. He'd been a decent player for Marseille but looked like another of those random buy-to-sell deals that Chelsea loved so much.
He soon became the starting right-back, then the starting left-back, then the starting centre-back, then went back to the right and is now shining centrally once again. If there was a gap in the team, Azpilicueta would fill it.
The current captain of Chelsea, Azpilicueta has won every trophy available to him in ten years at the Bridge and will forever be remembered as one of the Premier League's best bargains.
12. Eden Hazard
Hazard was one of the hottest talents in world football when he joined after the 2012 Champions League triumph, and he quickly emerged as one of the game's standout players. While never hitting the levels of Cristiano Ronaldo or Lionel Messi, Hazard was regularly touted as the third-best player in the world during his prime.
Chelsea haven't had many players better than Hazard, who would often drag the team to success even when they weren't playing particularly well. He was an absolute wizard with the ball at his feet and convinced Real Madrid to spend a whopping £100m to sign him in 2019.
Before Hazard left, he won two Premier League titles and three more domestic cups, leaving a bigger legacy than his trophy cabinet may suggest.
13. Cesc Fabregas
Fabregas' move to Chelsea in 2014 took everyone by surprise. The Blues moved quickly and aggressively to bring the former Arsenal man back to London, and he justified that with his performances on the pitch.
In his competitive debut, Fabregas pulled out one of the Premier League's most famous assists, dinking the ball through to Andre Schurrle to open his account for the club.
Fabregas remained a star for the club until his departure in 2018, getting his hands on two Premier League titles.
14. N'Golo Kante
Appearances: 244 (ongoing)
Leicester were the ones to pluck Kante out of obscurity, but after turning him into one of the world's best midfielders, they sold him to Chelsea for a ludicrously cheap £32m in 2016 - the same summer that Man Utd spent £89m on Paul Pogba.
Kante has been absolutely sensational for Chelsea and finished fifth in the Ballon d'Or voting as recently as 2021 after winning man of the match awards in the Champions League semi-finals and final.
He's shone in so many systems and continues to defy all logic to this day.
15. Thiago Silva
Appearances: 65 (ongoing)
Silva's Chelsea career is still young and it's not going to last much longer, but we're talking about one of the all-time great defenders joining on a free transfer. What more could you ask for?
The veteran Brazilian quickly established himself as one of the best defenders in the Premier League and played an integral part in leading Chelsea to Champions League glory under Thomas Tuchel.
He's not going to win as many trophies over as many years as some players who haven't made this list, but there won't be many who leave his sort of impact.