Billy, Legend of Ooo and Finn's idol

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  Billy is left-handed.

  The Lich used Billy's carcass as a disguise to gain entrance to the Time Room after killing him

  In earlier versions of the storyboard, Billy was named "Hogarth."

  

  Billy's sword is named "Nothung" (pronounced No-Tongue) after the sword belonging first to Siegmund and later Siegfried from Richard Wagner's cycle of operas Der Ring des Nibelungen (The Ring of the Nibelung). Billy has the ability to call his sword by saying its name. He retains the ability to do this even when he is old.

  

  Billy is voiced by Lou Ferrigno, who also played The Incredible Hulk in the live action TV series from the 1970s.

  Lou Ferrigno is partially deaf, which causes his speech to sound slurred. This resulted in Billy speaking with a lisp.

  

  Billy's appearance in the "His Hero" title card is based on Frank Frazetta's painting "Death Dealer." 

  On some concept art for Adventure Time, Billy can be seen breaking one horn off the Lich's helmet.

  

  Both Finn and Billy have many things in common: their arch enemies are rulers of elemental kingdoms (Ice King and Fire Count) and always capture Princesses, the Princesses most saved are from the Candy Kingdom (Princess Bubblegum and Cotton Candy Princess), both of whom gave the hero a piece of their hair. They both keep piles of treasure in their homes too. They both also have had a magical dog at their side, Jake and the unnamed dog corpse in Billy's lair. They can both play the flute.

  

  Jake stated before that he has a secret crush on Billy.

  Billy has six fingers, while the show's characters are commonly portrayed with four fingers. His gauntlet also has six fingers. Considering his large stature and the number of fingers he possesses, Billy could possibly be a Nephilim, or at least a reference to the legend.

  Billy is confirmed to be dead by Prismo in "Finn the Human," when he describes the Lich as "a ghost wearing a dead guy."

  

  He is the first recurring character to die.

  It is unknown how Billy knew about Finn's biological father, Martin.

  Billy was also shown trying to avoid telling Finn about Martin and only did so after Finn insisted, likely because he did not want Finn to know that his father was a criminal.