Aguero scored 20 goals in La Liga for Atletico last season
Sergio Aguero has signed a five-year contract to complete his move from Atletico Madrid to Manchester City.
The Argentina international, 23, had arrived in England on Wednesday to finalise the transfer for a reported £38m.
On Thursday evening the Eastlands club announced the deal was done, and that Aguero would wear number 16.
The club said the striker was likely to be in their squad for the weekend's Dublin Super Cup tournament.
Earlier on Thursday, Aguero had Tweeted: "I'm already a City player. Happy to be in this club and this city."
City pressed on with the move despite the collapse of Carlos Tevez's proposed switch to Corinthians.
The striker, nicknamed 'Kun', also interested Real Madrid and Juventus but has become the most expensive signing in City's history, eclipsing the £32.5m paid for Robinho in 2008.
Neither Real nor Juventus met Atletico's valuation of the striker.
Aguero flew in from Buenos Aires, via Heathrow, early on Wednesday morning and went straight to a private Manchester hospital to undergo his medical.
He then had a brief stop at City's stadium in the early evening, and, after holding discussions with City officials, he happily signed autographs for the growing crowd of fans who had gathered.
Corinthians, meanwhile, pulled out of their bid to take Tevez back to Brazil last week after initially agreeing a £38.6m transfer.
That translated as 40m euros plus 4m euros in add-ons and City were happy to accept payment in instalments as part of the deal, but Corinthians were unable or unwilling to provide the customary bank guarantees associated with a deal of such magnitude.
Tevez's desire to leave City remains as strong as ever, but he may face an added complication as City are unlikely to accept a similar fee to that offered by Corinthians from any of the top European clubs considering an approach for the 27-year-old Argentine.
