Eto'o shone under Mourinho during Inter's Champions League-winning 2009-10 season, before becoming the highest-paid player in the world - earning a reported €300,000 (£167,825) a week - when he moved to Anzhi and is delighted to be reunited with the Chelsea boss.
Jose Mourinho has tracked Wayne Rooney for much of the summer, with two bids rejected, but has now moved for the 32-year-old after abandoning his pursuit of the Manchester United man.
"I am very happy to be here but also anxious because I want to get playing as soon as possible," he told the club's official website.
"It wasn't a hard decision. I saw the qualities Chelsea have, and I was very happy with Jose Mourinho before, so when the opportunity came, I was very happy to take it."
Eto'o becomes Chelsea's second summer recruit from the Russia outfit after Willian's arrival on Wednesday for £31.7m, joining Cristian Cuevas, Andre Schurrle, Mark Schwarzer and Marco van Ginkel at Stamford Bridge./Goal.Com/