Which player lays claim to the iconic name and why are they most deserving of the title? Let's take a look.
The names of the most gifted footballers to ever play the game usually roll off the tongue.
Diego Maradona. Johan Cruyff. Zinedine Zidane. Lionel Messi. People are rarely left in doubt when they hear those words uttered.
However, mention the name 'Ronaldo' and more often than not you run the risk of being asked, "which Ronaldo? The real Ronaldo, or...?"
Who is 'the real Ronaldo?'
When people refer to the 'real Ronaldo' they generally mean Ronaldo Luis Nazario de Lima, the Brazilian footballer who was born in 1975.
The use of the prefix 'real' became widespread in the early-to-mid 2000s during rise to prominence of the Portuguese footballer Cristiano Ronaldo in order to distinguish between the two players.
Of course, in describing Ronaldo Nazario as the 'real' Ronaldo it was both a term of deference to the elder of the pair and inherently dismissive of the the younger.
Ronaldo Nazario, nicknamed O Fenomeno (meaning 'The Phenomenon' in Portuguese) had by that stage established himself as one of the best footballers in the world by scoring hundreds of goals, scooping two Ballons d'Or and three FIFA World Player of the Year awards.
He had starred at home for Cruzeiro before building his reputation as the most fearsome striker in world football at PSV, Barcelona, Inter and Real Madrid. The 'real Ronaldo' was therefore, for some, the genuine article and his glittering career warranted that he and he alone should lay claim to the name.
However, as the powers of Ronaldo Nazario declined later in his career and those of Cristiano Ronaldo grew stronger, the debate over who should be considered the 'real Ronaldo' began to rage.
In truth, when their careers are set against one another now, the Portuguese has far exceeded his Brazilian counterpart and for a younger generation of football fans he is 'the real Ronaldo'.
Indeed, Cristiano Ronaldo evolved into the most prolific goalscorer in football, smashing record after record on his way to success with Manchester United, Real Madrid and Portugal.
There is no comparison between the two when it comes to goals scored at both club and international level either, with the Portuguese scoring roughly double that of the Brazilian - helped, no doubt, by his superior longevity.
Similarities between Ronaldo Nazario & Cristiano Ronaldo
Aside from their names, there are a number of similarities between Ronaldo Nazario and Cristiano Ronaldo.
Long before the brand CR7, for example, Ronaldo Nazario and 'R9' were synonymous, with the Brazilian launching a personalised style of boots.
They are players who both starred as the face of Nike's football range over the years, appearing in advertisements and promotional imagery.
While Cristiano Ronaldo began his career as a winger, he eventually transformed into a complete forward, playing more in a central role, much as Ronaldo Nazario did.
Other footballers called Ronaldo
Ronaldo is a popular name in Brazil and Portugal and the debate over players called Ronaldo did not begin with Ronaldo Nazario and Cristiano Ronaldo.
Interestingly, Ronaldo Nazario was briefly known as 'Ronaldinho' in the early 1990s in order to distinguish him from Ronaldo Rodrigues de Jesus who was also playing for Brazil.
Ronaldo Rodrigues later became known as Ronaldao.
Ronaldo de Assis Moreira is another famous Ronaldo in football, though he is better known by the name Ronaldinho.