Blackburn Rovers manager Sam Allardyce (Photo; AP)
West Ham owners David Sullivan and David Gold have turned to the 56-year-old Allardyce to guide them back to the lucrative Premier League at the first attempt.
"It's a fantastic club with a great tradition and loyal supporters," said Allardyce.
"I am determined to get this club back up."
Allardyce added on the club's official website, www.whufc.com: "I wouldn't have taken this job if I didn't think we could bounce straight back into the Premier League.
"More than that, I wouldn't have contemplated the job if I didn't think there was the opportunity to build something substantial at West Ham.
"I know there will be West Ham fans asking whether I'm going to abandon the style of play that's been the club's heritage over the years.
"All I'll say is it will be a tale of home and away. At Upton Park we'll try to play the kind of game the fans want.
"We will aim to continue in the same way on our travels but we'll also be tough, hard to beat and utterly resilient."
The new boss at Upton Park has reportedly been offered a huge bonus to guide West Ham back to the big time.
This is Allardyce's first job since he was surprisingly sacked as manager of top-flight Blackburn Rovers in December, and it is the first time in 10 years he has taken over a club outside the top flight.
Allardyce began as a manager with spells at Blackpool and Notts County before making his reputation at Bolton Wanderers after taking them into the Premier League via the playoffs in 2001 and establishing them in the top tier of English football.
He then moved to Newcastle in 2007.
But the owners who appointed him sold up soon afterwards and he was sacked by Mike Ashley just six months into his time with the north-east side.
It was a similar story at Blackburn, where he took charge in December 2008 only to be dismissed not long after the club was sold to Venky's, an India-based poultry business.
Grant was axed minutes after West Ham's relegation was sealed by a 3-2 defeat at Wigan a week before the end of the season.
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