David Moyes said he has a point to prove and is "hungry to get things right" after being appointed as West Ham's new manager.
The former Everton and Manchester United boss replaces Slaven Bilic, who was sacked on Monday with the Hammers in the relegation zone.
Moyes has been out of work since May, when he resigned as Sunderland manager after the club's relegation to the Championship.
West Ham joint chairman David Sullivan said the 54-year-old Scot is "the right man to turn things around".
He added: "We need somebody with experience, knowledge of the Premier League and the players in it, and we believe David can get the best out of the players.
"He is highly regarded and respected within the game and will bring fresh ideas, organisation and enthusiasm.
"He proved with Everton that he has great qualities and we feel that West Ham United is a club that will give David the platform to display those qualities again."
Moyes' first game in charge will be at Watford in the Premier League on 19 November.
He added: "I've managed five clubs since starting out nearly 20 years ago at Preston and then going to Everton. My period at Manchester United is well documented and I then did something I have always wanted to do by experiencing management abroad, with Real Sociedad.
"It's only been the last job where I feel it wasn't a good move and I didn't enjoy the experience. So I'm hungry to make sure I get things right now.
"I don't know any manager who hasn't gone through negative periods, especially in the game today. I hope it gives me great strength and understanding of what is required."
What does Moyes face at West Ham?
The Hammers are 18th, having won just two Premier League matches in 2017-18 - and lost their first three league games of the campaign.
Bilic spent a reported £42m on players in the summer - including forward Marko Arnautovic from Stoke City for a club record £20m and former Manchester United striker Javier Hernandez from Bayer Leverkusen for £16m.
But West Ham have taken just nine points from 11 league matches, conceding 23 goals.
Following the Watford match, West Ham host Leicester City and go to Everton, before a difficult run in December which brings league games against leaders Manchester City, last season's champions Chelsea and Arsenal.
Later in the month, the Hammers travel to face the Gunners in the Carabao Cup quarter-finals.
West Ham's forthcoming fixtures 19 November: Watford (a); 24 November: Leicester City (h); 29 November: Everton (a) 3 December: Manchester City (a); 9 December: Chelsea (h); 13 December: Arsenal (a)
What is Moyes' track record?
Moyes, who started his managerial career at Preston North End, was voted LMA Manager of the Year three times during an 11-year spell at Everton from 2002 to 2013. In 11 full seasons, the Toffees finished in the top eight nine times.
He succeeded Sir Alex Ferguson as Manchester United boss on his fellow Scot's recommendation when he retired after a trophy-laden 26 years in charge at Old Trafford.
But despite signing a six-year deal with the then Premier League champions in 2013, he was sacked 10 months later with United seventh in the table.
Moyes went on to manage Real Sociedad in Spain but was sacked by the La Liga club after a year in charge in November 2015.
He took over at Sunderland in July 2016 before quitting in May 2017 after the Blacks Cats were relegated, having finished bottom of the Premier League.
Former West Ham striker Dean Ashton told BBC Radio 5 live that Moyes was "the safe option if you're thinking about grinding out until the end of the season and safety".
But he added: "As a player, David Moyes coming in wouldn't inspire me."
'Belittling, disrespectful, everyday sexism'
During his time at Sunderland, Moyes attracted controversy for telling BBC reporter Vicki Sparks she might "get a slap" in March, leading to a Football Association charge for improper conduct and a £30,000 fine.
He said he "deeply regrets" making the comment and later apologised to Sparks, who did not make a complaint.
Writing in her Sun column in April, West Ham's vice-chairman Karren Brady said Moyes' words were "just another brilliant example of the pressure women are under to laugh off these everyday moments of sexism as a joke".
She added: "The threat to give someone a slap, no matter how you look at it, is aggressive. It is not banter. And it is not OK.
"I would like to think that any man who worked for me - no matter how wound up they feel by a reporter who is simply doing her job well - would not threaten to slap a woman.
"One of things I find most objectionable in this whole story is his reference to Sparks as being a 'girl', when he said he had apologised to her.
"She's not a girl. She is a woman and a professional. To call someone a girl is belittling, disrespectful and a real indication that you don't see her as an equal.
"Hopefully the penny has dropped for him that it's not OK to patronise, intimidate and threaten women and treat them as if they are imposters in a man's world."
Moyes' arrival at West Ham has not been greeted with overwhelming enthusiasm by the club's support, something owners David Sullivan and David Gold are aware of.
However, it is the Scot's diligence on the training ground that is understood to be the major attraction in the decision.
West Ham spent in excess of £40m in the summer to sign former Manchester United striker Javier Hernandez, Manchester City pair Pablo Zabaleta and Joe Hart, and Stoke's Marko Arnautovic, who cost a club record £20m.
But, as a collective, West Ham have badly underperformed.
Sullivan and Gold feel they need someone to galvanise the current group of players rather than spending more money on completely revamping the squad.
What do the fans say?
Graeme Howlett, editor of the West Ham fans' website Knees Up Mother Brown
The fans seem quite unanimous in that they are not particularly keen to see Moyes come in. They would prefer to see someone more progressive.
I suspect there will be an awful lot of criticism for the board, who are already under intense pressure following the move to the Olympic Stadium, which has not gone down well.
Various reasons have been mentioned, including his record at Sunderland, where he came in at a similar position and failed to keep them in the Premier League. There was also the incident with the female reporter which has been mentioned a few times.
I hope he does well , but He has a tough job on his hands
When he was being interviewed by Andy Gray and Richard Keys, he was asked if he was interested in that job, and said Yes. This was before Bilic had been sacked, which I thought was poor, but maybe he already knew.