#1 Summer 2009
Cristiano Ronaldo. Do we really need any other reason?
In his career at Madrid so far, Ronaldo has stopped defences in their tracks, shifted entire fan demographics, and has broken literally every goalscoring record known to man.
£80 million in 2009 was an eye-popping large fee, even for a player who had just won the Ballon d'Or and the Champions League.
But, considering that players like Oxlade-Chamberlain are going for £40 million, Ronaldo's fee seems like pennies right now. And while we sing praises of the Portuguese superstar, let's not forget that other summer signings included Kaka, Xabi Alonso, Karim Benzema and Alvaro Arbeloa.
Even though Kaka always had an impact whenever he played, he was almost criminally underused by Mourinho, although a spate of injuries also contributed to that.
For all the constant criticism that Karim Benzema receives, he brings his own set of qualities whenever he steps out on the pitch, and has struck up a very good relationship with Ronaldo that has reaped benefits for Real.
Alonso arrived at Real Madrid having already established himself as one of the best holding midfielders in the world at Liverpool. In the five seasons he spent at the Bernabeu, he was almost always in the starting XI, winning the La Liga and the Champions League before eventually moving to Bayern to 2014.
Granero, Negredo and Garay might not have had the intended impact, but Ronaldo's name alone is enough to make the summer of 2009 one of the best periods of transfer business conducted by Real Madrid in their 116-year history.