Dr. Pierre Aronnax is a French naturalist and lecturer at the Museum of Natural History in Paris. In the summer of 1866, when sightings of a mysterious sea monster are being reported, he is in the United States doing research. The author of a two-volume book on underwater life called The Mysteries of the Ocean Deeps, he is considered an authority on sea life, and so he is invited to join an expedition to hunt the creature. Just as the expedition is about to be abandoned, the warship attacks what its crew believes to be the sea monster. During the action Dr. Aronnax is knocked overboard and received by the "monster"—actually a submarine called the Nautilus. He is held captive on the vessel for nearly 10 months. At first he is awestruck by the opportunity to explore underneath the seas, but eventually he tires of it and comes to resent the enigmatic Captain Nemo.
Captain Nemo, whose name is Latin for nobody, has renounced civilization, choosing instead to spend his life traveling the seven seas on his submarine. He reveals almost nothing about his past to his three visitor-captives from the Abraham Lincoln, but he does tell Dr. Aronnax he trained as an engineer. He is extraordinarily intelligent and usually remarkably self-composed, but he is given to bouts of severe moodiness. He occasionally alludes to traumatic events from earlier in his life, but by the end of the story, Dr. Aronnax knows almost nothing more about him than he did the day they met.
Conseil has been accompanying and assisting Dr. Aronnax for 10 years. Their travels have taken them to China and the Congo, among other places. He is so loyal to Dr. Aronnax that he puts himself in harm's way multiple times to assist the older, frailer professor. He is extremely witty and, except for a few instances, remarkably good-natured and stoic.
A true man's man, Ned Land loves hunting, meat, and sailing over rough seas. Temperamentally, he's the complete opposite of Conseil: hotheaded, impulsive, and immature. Still, he is a loyal friend to Conseil and Dr. Aronnax during their journey/imprisonment aboard the Nautilus, and he helps save Dr. Aronnax's life more than once. He is the first of the men to rebel against their imprisonment in the submarine. As the journey stretches out, he gets increasingly homesick and desperate.