Sir Alex Ferguson confirmed this morning that he will step down from his position as manager of Manchester United at the end of the season.

During his 27 years at the helm, the Scot has made a large number of successful acquisitions in the transfer market.

With that in mind, Sports Mole has selected what we believe to be five of the best signings to arrive at Old Trafford during Ferguson's time in charge.

5. Robin van Persie - 2012

Having seen his side lose the title to rivals Manchester City in dramatic fashion on the final day of the season in 2012, Ferguson insisted that he would not allow that to happen again. He was true to his word by purchasing Robin van Persie for £24m from Arsenal and the Dutch striker has played a big part in helping the club regain the Premier League trophy in what has proved to be the 71-year-old's last season in charge.

4. Peter Schmeichel - 1991

Ever since Ferguson had taken charge of the club in 1986, he had struggled to find a dominating goalkeeper. His search ended in 1991 when he finally landed Schmeichel from Brondby - a year later than he had wanted to. 'The Great Dane' went on to play a major role in five Premier League title wins, culminating in success in the Champions League in 1999.

3. Roy Keane - 1993

Throughout the 1980s, Bryan Robson had often carried United. As the Premier League era got underway though, it was clear that 'Captain Marvel' was not the force that he once was. That prompted Ferguson to sign Keane from Nottingham Forest and the Republic of Ireland player set the tone on his debut by scoring twice against Sheffield United. Following the departure of Eric Cantona, he took over the captaincy and led the club to numerous trophies.

2. Cristiano Ronaldo - 2003

Ferguson displayed his ruthless side earlier in the summer of 2003 by allowing David Beckham to join Real Madrid. However, a curly-haired youngster with a liking for a step-over was signed from Sporting Lisbon and in time the United supporters had a new hero. He realised his potential as United won the title in 2007 and was their talisman as they lifted the Champions League trophy a year later. He was sold in 2009 to Real Madrid for a world record fee of £80m - a handsome profit on the £12.6m that the club paid for him.

1. Eric Cantona - 1992

There was always a feeling around the time that United would finally end their wait that had stretched back to 1967 to win a league title. However, without the signing of Cantona from Leeds United, it may have taken even longer. The Frenchman provided that touch of class that was lacking and he went on to form a strong partnership with Mark Hughes. Later on, he became the teammate and captain that the likes of Beckham, Paul Scholes and the Nevilles looked up to. Had he not have joined United, their history could well be different and all for a reported £1.2m.