Mr. Okamoto and Mr. Chiba identify the blind Frenchman, who sails up to Pi late in the telling of the first story, as the hyena. This complicates the allegory, but, like we said, it's not exactly your standard allegory (see "Symbols, Imagery, Allegory").
So: how can the hyena be both the cook and the Frenchman? Well, Mr. Okamoto and Mr. Chiba think that since Pi kills the cook and Richard Parker kills the hyena and the blind Frenchman, Pi has mapped the both the hyena and blind Frenchman onto the cook. Also, the Frenchman – though at this point Pi thinks Richard Parker is speaking – admits to having killed two people, just like the cook did.
Should we trust those pesky investigators? We're not sure. Pi, in a delirium of starvation and guilt, could very well have imagined the blind Frenchman.
We have no simple answers...and the book doesn't exactly throw us a bone. The blind Frenchman does highlight Pi's madness and the depravity of cannibalism (which, if we must remind you, your dear Pi commits). Perhaps it's a good thing Richard Parker gets rid of this Frenchman quickly: he complicates the allegory and perhaps represents the evil that Richard Parker, through his own violence, dispatches.