Professor Arronax is the story's narrator. Consequently, he is also the main protagonist; however, that has always struck me as odd. Most people would say that 20,000 Leagues Under the Sea is a story about Nemo—rather than it being a story about Arronax and his time with Nemo. This is probably because Arronax isn't an easy person to like. Nemo is far more mysterious and charismatic. Arronax is more often than not arrogant, and this doesn't endear him to readers. He too often thinks that he is the smartest person in the room. He also doubts nearly everything that he himself isn't capable of doing or thinking.:

That a private individual had at his disposition a mechanical contrivance of this sort was improbable. When and where could he have had it built, and how could he have kept its construction secret?

Arronax also is a man that enjoys having everybody praise his supreme knowledge. He admits that he wants to make sure the world knows about his adventures and the knowledge that he gained from the Nautilus. He wants the praise. It's not until the novel's conclusion that readers see Arronax move past his arrogance and do what is right (rather than pursue what knowledge might gain himself more praise).

Professor Aronnax is the main character and narrator of 20,000 Leagues under the Sea. He is a marine biologist, a leading scientist and expert on the subject, whose intellectual curiosity is piqued by tales of a giant sea-monster wreaking havoc on international shipping lanes. The American government is so concerned by the damage that his giant creature is doing to international trade, that it puts together an expedition to hunt down the monster. Aronnax joins the expedition at the last minute, and serves in the capacity of a scientific observer.

He thinks that the sea-monster might be a giant mutant strain of narwhal, a medium-sized whale renowned for the single tusk that protrudes from its bulbous head. There's no doubt that Professor Aronnax is something of a glory-hunter; he sees the expedition as an opportunity to achieve lasting fame and renown, to go down in history as a great biologist who made an earth-shattering scientific discovery that changed man's understanding of the natural world forever.