Pantherk is a fighter from M.U.G.E.N who is a panther-human hybrid. He is disregarded for being a poorly-designed fighter, being overpowered and having simplistic animations. His appearance seems to just be a warrior fighter in a blue skin with a panther head photoshopped on.
Since Joel's stream of Mortal Kombat Chaotic, Pantherk has become a meme within his fanbase.
Ironically as of Mortal Kombat 11, actual character Kotal Kahn has the ability to morph into a panther.