Furnius

Furnius is the nephew of Flame King. His father was killed by the Flame King in order to take the throne. As a result of this, Furnius and his brother Torcho attempted to assassinate their uncle by pouring ice over him as he watched a play, but were foiled by Finn and Jake who overheard them discussing their target and decided to intervene on their assassination.

Furnius has a forked tongue, thus, he speaks with a hiss inflection in his voice. Finn and Jake use this recognizable trait to track him down since they had yet to see his appearance after hearing him talk about his plot to Torcho, and this leads them to accidentally mistake Jalapeño pepper for him when a snake on Finn's shoulder hisses as Jalapeño pepper speaks. Eventually Furnius' hissing enables Finn to recognize him as the conspirator when he is disguised as an executioner. After Torcho and Furnius' plot is exposed, they are both put in a "punishment room."