Shigeru Miyamoto is arguably the world's most famous game designer, and not someone you'd want to set yourself against in a professional capacity.
However, Nintendo president Satoru Iwata has admitted in a recently-translated interview with 4Gamer that when he was starting out in the industry, he decided to make Mario's dad his rival:
"So, I have this strange sense of duty regarding the codifying of the 'Miyamoto Methodology', because I feel like it would be useful to the game industry if you could put it into words. I started up a project similar to 'Iwata Asks' for that purpose. And, of course, wanted to see it put into words so I could understand it too, because back when I was just starting out, I sort of arbitrarily decided that Miyamoto was my rival, though that's embarrassing to admit now.
Would you believe that for a long time I'd just decided within myself, completely arbitrarily and not at all reciprocated, that he was my rival and I wanted to do something to just give him hell."