Lionel Messi and Cristiano Ronaldo: you can't have a debate about their greatness without comparing them to each other. Much like the Joker and Batman, polar opposites who are defined in each other's image, we've come to assess Messi and Ronaldo against each other, not in a vacuum but as a tandem. It's the privilege and curse that comes with being the two best players on the planet right now.
We were reminded of this dynamic at the start of Euro 2016, when Iceland defender Kari Arnason pointedly cited Messi in order to get further under Ronaldo's skin, after the Portuguese's uncharitable comments about the Icelandic team.