The former Middlesbrough wide-man scored nine goals in 63 league appearances for the Villa Park outfit after arriving for £12 million in July 2009.
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Kenny Dalglish's side are believed to have paid £20 million to acquire the services of the England international, who has won 27 caps for his country.
And Houllier, who has been forced to stand down from his post as Villa boss due to health reasons, is confident Downing will prove a big hit on Merseyside, providing the crosses for £35 million signing from Newcastle United, Andy Carroll.
"Stewart will fit in very well at Liverpool. I like him very much as a player and I am certain he will be a very big asset to them," he said in The Sun.
"Stewart is a very modern player. He can attack and defend and was involved in so many goals for Villa last season.
"He is one of the best crossers of a ball in the Premier League with his right or left foot and is very skilful."
Downing supplied the second highest amount of crosses in the Premier League in 2010/11, with only Everton full-back Leighton Baines (351) delivering more than Liverpool's new recruit.
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