|“||♪ Whose the greatest warrior ever, a hero of renown, who slayed an evil ocean, who cast the Lich King down? Billy! ♪||„|
Finn and Jake eventually meet their hero but find he has not only retired but that had lost heart in adventuring. Billy says that beating up evil is only a temporary solution because it is always replaced by some new evil and people keep getting into trouble. Billy encourages Finn and Jake to stop resorting to violence and help society by volunteering for community service. After trying, and failing, to help society with non-violent aid Finn stops a rampaging monster by beating it up and realizes sometimes violence is the answer and he goes to Billy with his new revelation. Once Billy sees the old woman saved he realizes that such efforts do in fact pay-off and thanks Finn for reminding him of the importance of fighting the good fight.
Billy's history with the Lich eventually catches up with him, when the Lich is accidentally freed Finn and Jake set out to stop him with the sword of Billy. The Lich is defeated eventually but escapes death by possessing Prince Bubblegum at first and then later a snail once it is driven out of Princess Bubblegum. With some help the Lich is able to get his hands on the Enchridion, an ancient book that catalogs the secrets of heroes. Once he has the Enchiridion the Lich confronts Billy killing him and his friends. Upon killing him the Lich possesses Billy's body and uses the guise to con Finn and Jake into helping him open a portal between time and space to a realm where he will be granted a single wish. By the time Finn and Jake catch on to the Lich's trick the portal is already opened and the Lich in Billy goes to make his wish. Finn and Jake use their wishes to unmake the Lich's. When last seen, Billy's body was still possessed by the Lich and trapped in the pocket dimension having wasted his wish. Later though Billy's spirit is revealed to be at peace and thanks Finn after Finn completed his bucket list for him. With Billy's final words before he goes on to 50th Deadworld (heaven) BIlly revealed to Finn that his biological father was alive.