The 27-year-old spent six years at Old Trafford prior to his world record ₤80million switch to Madrid in the summer of 2009.
During his time with United, Ronaldo matured from a fleet-footed teen winger into a goalscoring machine, breaking George Best's 32-year record for most goals scored by a midfielder in the red shirt with 42 in the 2007-2008 campaign.
That saw the Portuguese land the coveted European Golden Shoe and later that year the World Player of the Year Accolade as he inspired United to a Premier League and Champions League double.
Since ending his love affair with the Red Devils to join boyhood heroes Madrid, Ronaldo has gone from strength-to-strength, rewriting yet more records at the Bernabeu with his goalscoring feats.
Indeed, in his three years with Madrid Ronaldo has netted a remarkable 146 goals in all competitions, a figure made even more impressive by the fact it has come in just 144 games, giving him a goals to games ratio of 1.01.
Having helped Madrid to a first La Liga title in four years last season, ending Barcelona's monopoly in the process, it's perhaps no surprise Ronaldo is so content with life in the Spanish capital.
While he recently spoke of missing his "United family", Ronaldo has always maintained he is happy in Madrid and admitted as much on a trip to Dubai  late last year.
A return to United had long been mooted, despite Carlos Queiroz, Ronaldo's compatriot and former Madrid boss and No.2 at Old Trafford, telling Sport360° in an exclusive interview last year that Ronaldo would never return to his former stomping ground.
"No, I don't believe he will return," said Queiroz. "He is very happy in Madrid and playing incredibly well. United is a closed chapter in his career and he is focused on winning titles with Madrid."
And so it appears to be the case with Ronaldo confirming in an in-depth article with Madrid-daily Marca that he is indeed intent on hanging up his boots with Los Blancos. "I am honest. And I will look into your eyes when I say I want to retire at Real Madrid," said Ronaldo.
While it appears Ronaldo is content off the pitch, on it, he is refusing to rest on his laurels despite another trophy-winning season after Madrid ended "Barcelona's streak" and collecting yet more personal accolades.
Ronaldo netted 46 goals in just 38 La Liga games last season, but he is determined to better that figure next term as he eyes further success with the club. "I always want to improve, I will try to beat my numbers this season."