When King Trevor was a child, he was always looking to humiliate King Frederic to participate in his jokes and pranks, but King Frederic said he was not to participate.
He has a pet seal named Trevor Jr. which he overprotects, evident by its reluctance to reunite with Trevor after Flynn and King Frederic are captured and locked up and its glee when Trevor falls down his own trapdoor, although it is shown at the end of the episode to be free. Although he is a king, his attitude is that of a vengeful child.
Role in the series
In "In Like Flynn", King Trevor sends his agents to Corona to deface King Frederic's statue with graffiti and a sign reading, "Equis Rules". Finally fed up with the neverending humiliation from Trevor, King Frederic proposes to Eugene to steal the royal seal of Equis to humiliate King Trevor, but they were captured by the guards.
After a conversation between Eugene and King Frederic, King Trevor came in the jail room with his old seal Trevor Jr, Frederic told him to release Eugene and himself. King Trevor told him he intended to only after parading his rival in nothing but a jester's hat, showing that Equis was "superior" to Corona. He then left the duo to wallow in the stench of their own defeat.
When King Frederic and Eugene escaped from jail, they run into King Trevor and improvise by tricking him into stumbling through his own library's trapdoor. At Eugene's suggestion, they further humiliate him by leaving King Trevor tied to his own statue with nothing but a jester's hat and a sign reading "Corona Rules" in plain view of his subjects.