Okay, guys, let's get the obvious out of the way first. Conseil means counsel, in French, which is pretty ironic. This guy is basically in the book to serve his master, Aronnax (and be his trusty life-saver, we might add). He would never deign to advise his master.
And, as you may have noticed, Conseil really, really loves Aronnax. His dedication to the guy, at the cost of his own survival instincts, makes us kind of uncomfortable, actually. Conseil just seems to think whatever his master thinks, and do whatever his master does.
There are plenty of examples of Conseil's servile behavior. Like how he jumps in after Aronnax when he's thrown overboard, and helps him survive, even though Aronnax is pretty much whining like a little baby the whole time.
But there's more to our boy Conseil than meets the eye. Beneath Conseil's loyal shell, and beyond his impressive, obsessive, bizarre ability to classify animals and plants—fish that he requires Aronnax to recognize first—lies a strange core.
Sometimes, Conseil's deficiencies are funny. Like when he can't believe that cod don't look like the filleted, gutted things you see in the fish market. Or when he decides to eat the fish that stings him "out of revenge," even though it tastes awful. But other times, they reveal a passion you wouldn't expect to find in a man who sometimes acts like a robot.
Take his reaction to the cannibal attack. On the one hand, he seems, how do we say this, non-judgmental. Sure, he compares savages to monkeys—you can't really forgive that little bit o' racism—but he also makes some surprisingly insightful statements. When Aronnax suggests that the "savages" must be "bad" because they're cannibals, Conseil replies:
One can be a cannibal and a good man […] just as one can be a glutton and honest. The one does not exclude the other. (1.22.46)
However, shortly after making this remark, Conseil nearly shoots one of the cannibals because a stone he's thrown breaks a rare shell. So we guess one can be kind of a thoughtful person and a master-serving oddball?
Above all, Conseil will always be Aronnax's loyal servant. But Conseil's eccentricities show us that there is more to this man who spends most of his time doing his master's bidding. He's not a one-dimensional dude.