Ronaldo is the main nerd in Mellowbrook. He usually counts on the laws of physics and mechanical engineering to help get him through all his problems. He is smart enough to create a car, as shown in "Mellowbrook Drift". He is one of Kick's rivals and was also in a romantic relationship with Kendall Perkins in some episodes.
Ronaldo has a very nerdy appearance. He has blond hair, wears glasses, and has a big head to show that he's smart. He tries to look cool by wearing a red and yellow hoodie (similar to Kick's jumpsuit), and black jeans with red boots. These clothes are perfect for when he does street racing.
Ronaldo is the science nerd of the series. He uses quantum physics and all sorts of smarts to aid in street racing which is his favorite hobby until he loses to Kick Buttowski in "Mellowbrook Drift". He depises Kick and Gunther and would do anything to see Kick kicked out of school forever. Ronaldo is also very judging as he loves to judge Kick's plans on how he will perform the stunt for when he builds or announces it. Ronaldo has a way of being a gloatful winner too as he gloats when he wins an event such as street racing, usually by means of cheating. He also gets away with things by using the good ol' Dine n' Dash routine in "Stand and Delivery" which almost runs Gunther's family out of business. But all is good as Ronaldo does have a soft spot for Kick and teaches him how to beat an extreme gameshow that has never been beaten before in "Faceplant!".
It is shown that he was in love with Kendall in "Frame Story". Kick found this out by accident when Ronaldo and Kendall go to the AV Department to talk about their love. He tries his best to impress Kendall, but at some point usually ends out horribly wrong with some things Kendall doesn't really like, such as writing a love poem entirely in binary or being too brainy instead of being more extreme.
Their relationship can also be seen in "Stand and Delivery", "Faceplant!", "Hand in Hand", "Detained", "Kick or Treat" and "Poll Position".
As seen in episodes like "Pool Daze" and "Gym Dandy" Ronaldo stands near Kendall but they aren't dating, in "Bromance", "Swap Meet" and "Goodbye, Gully" they are seen together in cameo roles, in "Big Mouth" they have an appearence but not together and is very possibly that they are no longer dating as of "Roll Reversal" because Ronaldo is impressed when Kick inadvertently becomes the smartest student in the class, and Kendall is jealous of Kick's accomplishment of the fastest record in a test.