|Parading: Eto'o has signed for Chelsea|
The 32-year-old Cameroon forward is understood to have signed a stunning £7million one-year deal, although he had to take a huge pay cut from the £17m a year which made him the world's best paid footballer at Anzhi Makhachkala.
Eto'o is apparently 'plan b' after Manchester United rejected two Chelsea bids for Wayne Rooney, with Mourinho opting against lodging a third, having said he had back-up options.
|Pen to paper: Eto'o signs the contract in the presence of Chelsea club secretary and director David Barnard|
The former Barcelona striker did not travel to Prague for Friday night's European Super Cup clash with Bayern Munich - neither did Willian, whose move from Anzhi was confirmed on Wednesday - but is eager to get into the action.
Eto'o, who will be reunited with Mourinho after the pair worked together at Inter Milan, said: 'I am very happy to be here but also anxious because I want to get playing as soon as possible.
|Pleased to be here: Eto'o has signed on a free transfer|
'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.
'I have had a career where I have been lucky enough to win a lot of trophies in different countries, but one of my last dreams as a professional is to come and play in England and see if I can have the same success as in my previous clubs.
'I don't see it as a final challenge, but to have a good time, enjoy my football, and have success with this team.'
Eto'o, who will have to wait until after the international break to make his debut, with Everton away on September 14 the first opportunity, revealed he might have been a Chelsea player sooner.
But he opted to stay at Barcelona before moving to Inter as part of the deal which saw Zlatan Ibrahimovic move in the opposite direction.
'I've had a couple of opportunities to come to England before, including the first time Jose was here, but it didn't work out for one reason or another,' Eto'o added.
The move might never have happened if Mourinho had received the indication from Rooney that he wanted to join Chelsea.
Speaking prior to confirmation of Eto'o's arrival, Mourinho appeared to have conceded defeat in the bid to capture England striker Rooney, who played for United against Chelsea on Monday and afterwards praised the 'fantastic' reception he received at Old Trafford.
Mourinho said: 'I told you what I have to say. I think I (made it) very, very clear that we didn't start the process (a third bid).
'We have nothing more to say. He's a Man United player and no more than that.'
Capturing Eto'o, who commanded wages reported to be in the region of £300,000 a week in Russia, is at odds with Chelsea's recent transfer policy of signing younger players. It also leaves a question mark over the futures of Demba Ba and Fernando Torres as Mourinho has made it clear four strikers is too many and that Romelu Lukaku is key for Chelsea's future.
Ba's place in the squad seems most at risk, but Torres has still to repay the £50million fee paid to Liverpool, as Mourinho admitted earlier this week.
Eto'o became Chelsea's fifth signing of the summer transfer window, following Andre Schurrle, Marco van Ginkel, Mark Schwarzer and Willian, who can be expected to provide the ammunition for the striker to score.
'I think Willian he is one of the best players in modern football,' Eto'o said.
The 32-year-old Eto'o began his career with Real Madrid before, following a spell with Real Mallorca, surging to prominence with Barcelona, scoring 152 goals in 232 appearances for the Catalan club.
He has a controversial history with Chelsea.
Following a bad-tempered Champions League encounter at Stamford Bridge, the striker criticised Mourinho, referee Pierluigi Collina and made a claim in the Spanish media that he was called a monkey by a Chelsea security guard. The allegations were swiftly denied by Chelsea.
It can be assumed Eto'o's relationship with Mourinho did not suffer as at Inter the pair combined to devastating effect and together won the 2010 Champions League title in a treble-winning campaign.
Eto'o, who also played at Stamford Bridge with Inter, added: 'They were always games between two big clubs. They didn't always finish well, but the most important thing is they were spectacular games every time.'
The striker netted 53 goals in 102 appearances for Inter before joining Anzhi in August 2011.