While not very well known, he is known for being a robot and that is pretty much all he cares about.
In his Nintendo Cinematic Universe portrayal, he is seen as mysterious agent. He watches over the heroes in the Nintendo Cinematic Universe, in hopes of one day being just like one of them. It is hinted he may have a crush on Samus Aran, however not confirmed.
R.O.B. appears in Robots Story as a playable character