He starts out as a big shot, headstrong teenager when he first appeared. He later became more of a concerned, heroic, and more courageous man, that Thumbelina needed. He is also very cocky, when battling Grundel the Toad, But most of All fell in love with Thumbelina (whom was flattering him, when she didn't notice he is the Prince).
He meets the tiny Thumbelina after she's just sung a heartfelt song about finding someone to love her, someone like her. Thumbelina is thrilled to meet someone her size, and someone like the fairies in her favorite books. Their attraction is immediate, and after brief introductions and some pretty heavy flirtation, Cornelius invites her on a ride on Buzzby, his trusty steed (a bumblebee). After their romantic musical nighttime dance, Thumbelina gives him a chain of forget-me-nots, asking him not to forget her. Cornelius promises that he never could, and says goodnight at her windowsill. When he returns, he finds she's been kidnapped. Mama Toad took Thumbelina to the lilypad showboat, where she promises Thumbelina as a bride to her buffoonish son, Grundel. Throwing caution to the wind, he goes on a reckless search for her, asking everyone and looking everywhere in an attempt to locate her as the winter approaches. His search is corrupted when a gust of wind blows him into a pond, and the frigid winter air freezes him almost instantly.
Some bug kids find him, and manage to get the block of ice out of the pond, and rig it over a fire, trying to melt the ice and free Cornelius. Once unfrozen, Cornelius appears just as Thumbelina runs away at the altar of her and Mr. Mole's marriage of convenience, battling Grundel and a mess of mob-mentality-driven wedding guests.
Thumbelina is flown by Jacquimo, the swallow, to a weed patch he's sure is the Vale of the Fairies. Thumbelina, jaded and upset at her long winter alone, and believing Cornelius is dead, disregards his optimism until Cornelius appears, victorious and shining with the springtime sun. Wings magically sprout from Thumbelina's back and the two are married in full fairy style.
He bears a resemblance to Harry Osborn, since Gary Imhoff the actor voiced him in Spider-Man the animated series, and was the co star of Christopher Daniel Barnes who also worked with Jodi Benson in the Little Mermaid.