5. Martin Skrtel (January 2008)
Despite being a Russian Premier League winner with Zenit St Petersburg, centre-back Martin Skrtel was relatively unknown in England when Rafael Benitez signed him in January 2008.
It was money well spent as the powerful and aggressive Slovakia international gave eight-and-a-half years of committed service to Liverpool, making 320 appearances and lifting the 2012 League Cup after scoring in the final against Cardiff City.
He served under five managers at Anfield - Benitez, Roy Hodgson, Kenny Dalglish, Brendan Rodgers and Jürgen Klopp - before eventually leaving to join Turkish side Fenerbahce in July 2016.