Fifi is General Viggo's pet human. He is a tiny, bald headed man who is most often seen being pampered by the General. He appears in most cutscenes with the General, usually getting attention or otherwise seeking it out for himself by rubbing up someone affectionately.
When the Fur Fighters attacked the Secret Island, Fifi guarded Viggo's key but it was seized by Rico. He later attacked Tweek in a carrier which the young dragon managed to blow up. This infuriated General Viggo, as he refers to the human as 'innocent little Fifi', despite the ill intentions the man had just shown Tweek. However, it is Fifi's demise that ultimately brings on the final battle.
Fifi was originally going to speak, though this was dropped fairly late in production. His voice appeared to have a German accent. 
Fifi is the only human in the game.
Fifi's appearance resembled Ernst Stavro Biofeld of the James Bond series. This is most likely reversed as General Viggo is most likely the white cat that Biofeld is seen stroking.