Winston the Ogre and Mrs. Ogre (Peter Vaughan and Katherine Helmond)
Well, folks, what we have here is a literal pair of monsters: an ogre and his wife who enjoy eating old shoes, boots, and occasional sentient beings who wander into their fishing nets. As with the other cameos in the film, they're mainly meant as a joke, in addition to being an obstacle that the gang needs to get around.
It's a tough balance to be funny but also threatening. Gilliam manages it first by giving the ogre all kinds of health problems that his loving but insistent wife makes sure he takes care of:
MRS. OGRE: Here we are, darling. Come on. And the ointment for the leg.
WINSTON: I grew too fast when I was young. That was the problem.
MRS. OGRE: You've been overdoing it a bit, dear.
WINSTON: You try being beastly and terrifying when you can only get one hour's sleep a night because your back hurts, and you daren't cough in case you pull a muscle.
MRS. OGRE: But you are horrible, dear.
WINSTON: You're just sayin' that.
MRS. OGRE: And gargle. Come on now, there's a good fellow.
These two are like every old married couple you've ever met: gently bickering, intimately familiar with each other, and absolutely devoted after a long, long period of time.
In light of that, their status as cannibals and monsters seems almost quaint. They're threatening, definitely, but at least they're kind of nice about it. It's a tricky balance, but it does make them real characters instead of just cutouts, and while we're not sorry they get chucked overboard, we're awfully glad they still get to be together.