This "Jester" person of his actually came about to counter-balance the blood lust inside of himself. Going off the werewolf stories more medieval era werewolves had "the beast" locked inside of them giving them a blood lust so like it's a voice in their head.

When he was young before "the beast" really developed in him he was a light hearted child. So when this odd voice appeared in the back of his mind he tried to make it go away with jokes, with silly light hearted things. This voice developed enough now though it's always there and it cracked his mind to the extent his jokester reaction to the voice got propelled and developed as him. So... He may or may not be insane... I think he's insane... Maybe just a little