Arsenal know all about Robin van Persie. After eight years at the club, the 29-year-old centre-forward left the Emirates to sign for Manchester United in the summer of 2012 and provided the missing piece of Sir Alex Ferguson's last title-winning jigsaw at Old Trafford.
Having narrowly missed out on the Premier League trophy at the end of the 2011-12 season (on goal difference to Manchester City), United knew they had to make a big signing that summer to give themselves any hope of dethroning City. But Van Persie, who had finished as the Premier League's top scorer with 30 goals, seemed an impossible target.