User blog comment:Kaido King of the Beasts/A Rival for Luffy/@comment-25501246-20160119151230

Pretty sure Eustass Kid and Trafalgar Law are supposed to be Luffy's rivals. That scene during Sabaody should have told us everything. Both are of the friendly competition type, although Kid is a bit more violent.

Blackbeard is probably the greatest example of a rival. They both share the same goal of becoming Pirate King. Again, that scene with them trying to one-up each other at Jaya should have told us everything. This one, however, is not friendly at all.

Coby, Smoker and other Marines don't exactly count as rivals, as a rival by definition has similar goals to the main character or at the very least share the same job (like Roger and Whitebeard).