Ron is 12 years old. He is the younger son of Russ Thompson, Sr. and Mae Thompson and younger brother of Russ Jr. He is often rude to his neighbor Nick Szalinski. After accidently hitting his baseball through the Szalinski's window, which unknowingly activates Wayne Szalinski's Shrinking Machine, Russ Jr. has him get it, but Ron along with Russ, Nick and the latter's sister Amy are accidently shrunk by the Shrinking machine. They are eventually returned to their normal size. By the end, he becomes friendly with Nick.
He is indirectly mentioned when Nick tells Mandy about the time himself Amy and his neighbors were shrunk.
Ron is rude, arrogant, worrisome, and selfish and can be blunt at times. He enjoys fishing and baseball. He is also a bully to Nick, but during their adventure, he warms toward him and finally becomes his friend. He is tough, but when Antie, the ant he befriended, died after being attacked by a scorpion, he broke down and cried. He's also known to be smarter than he gives himself credit for and has very creative ideas: such as being able to construct a booby trap in his backyard, using a crossbow, that fires a suction cup arrow, marked with superglue, rigged to Russ Sr.'s fishing rod, to catch intruders. As well as improving on Amy's earlier idea, which involved using a piece of cookie to lure Antie, by rigging it to a stick, which is then placed in front of the Ant, to make it follow it, while attaching a blade of grass to it, so it can tow Amy, Nick and Russ Jr..