Sir Alex Ferguson's 26 trophy-laden years at Manchester United saw some of the world's best players ply their trade at the club. Cristiano Ronaldo, Roy Keane, Wayne Rooney, David Beckham, Ryan Giggs, Paul Scholes and many more superstars donned the United jersey.Sir Alex Ferguson was named the world's best coach twice, in 1998 and 2007. He led Manchester United to 13 Premier League titles, two Champions Leagues, five FA Cups, four League Cups and a FIFA Club World Cup title.Many defenders made an impression under Sir Alex FergusonUnarguably the greatest manager in Premier League history, Sir Alex Ferguson once claimed, "attack wins you games, defense wins you titles." Naturally, the legendary manager's most successful Manchester United sides had great defenders, those who led the club to silverware.While some spent all their years representing United, some left a long-lasting impression in just a few years. In this article, we will look at the five greatest defenders who represented Manchester United under Sir Alex Ferguson.Honorable mentions: Gary Neville, Nemanja Vidic.#5 Denis IrwinDenis IrwinDenis Irwin joined Manchester United from Oldham Athletic and went on to spend 12 glorious years at the club. He first started as a right-back but soon made the left-back position his own, becoming a feature at the position under Sir Alex Ferguson.Irwin finished his time with Manchester United as one of their most decorated players, winning seven Premier League titles, a Champions League title, three FA Cups and a League Cup. He was an instrumental part of the treble-winning 1998-99 United side. In all, Irwin made 467 appearances for the club, scoring 33 and assisting 23 goals as well.arom_l@aroml_14Roy Keane on Denis Irwin: “My God, imagine if Denis Irwin was playing now. He could play left-back, right-back, get you a goal, knew how to defend, never injured, a brilliant guy in the dressing room. Denis would be world-class to me.”Happy bday Denis Irwin 🔴3:34 AM · Oct 31, 2021606Roy Keane on Denis Irwin: “My God, imagine if Denis Irwin was playing now. He could play left-back, right-back, get you a goal, knew how to defend, never injured, a brilliant guy in the dressing room. Denis would be world-class to me.”Happy bday Denis Irwin 🔴 https://t.co/DG3SKXQv6oA solid and hard-working defender, Irwin was one of the greatest defenders to have played under Sir Alex Ferguson. The legendary United manager was once asked to name his favorite United eleven. He struggled to find a spot for the plethora of stars that he managed, but here's what he had to say about Irwin:“But honestly, I would say Denis Irwin would be the one certainty to get in the team. I called him an eight out of 10.”#4 Gary PallisterGary PallisterGary Pallister was a fixture in the Manchester United side that dominated the early years of the Premier League under Sir Alex Ferguson. The centre-back played alongside Steve Bruce in the United back-line, helping the side win four Premier League titles and three FA Cups.Pallister made 337 appearances for the club in nine years after joining them in 1989. He was also named the PFA player of the year in 1992, a year before the start of the Premier League.🇾🇪The Fergie Years🇾🇪@Fergie_YearsSir Alex with Gary Pallister after his £2.3 million move from Middlesbrough in August 1989 which broke the english record for a fee paid for a defender. Superb value for money #MUFC1:41 AM · Oct 27, 202139424Sir Alex with Gary Pallister after his £2.3 million move from Middlesbrough in August 1989 which broke the english record for a fee paid for a defender. Superb value for money #MUFC https://t.co/WYxx9Z9WpPPallister left the club a legend, and his central defensive partnership with Steve Bruce is still talked about in glowing terms.