Stephen Maturin

On the Surprise, Stephen treats the wounded and the sick on a warship that lives in combat. After the Acheron's first attack, sick bay is packed, and he works nonstop.

But his mind is also somewhere else. Stephen collects insects, sketches animals and dreams of the Galápagos, islands almost no one has studied. To him, the voyage is a rare shot at seeing what no naturalist has seen.

Stephen and Jack couldn't be more different. Jack lives for the Navy, discipline and glory. Stephen distrusts war, rank and nearly every uniform. What binds them is music.

In the captain's cabin, with the cello between his knees, Stephen is the only man aboard who talks to Jack as an equal. He uses those moments to tell his friend, calmly and with no audience, what nobody else dares to say.

When Jack sets course for the Galápagos, he promises his friend time to explore the islands. The joy doesn't last. When he learns the Acheron is close, Jack breaks his word and keeps up the chase.

Stephen doesn't hide his anger. He accuses his friend of putting pride above good sense. They argue the way only old friends do, and then they go back to their violin and cello duets.

Captain Howard of the Marines aims at an albatross and hits Stephen in the stomach instead. The bullet drags a scrap of cloth into the wound, and getting all of it out is his only chance.

No one aboard has Stephen's skill. So he operates on himself, watching in a mirror, while Jack helps. The surgery works, and Jack gives up the chase so his friend can recover ashore.

Finally on the islands, Stephen collects everything he can. From a hilltop, he spots the Acheron anchored on the far side. He drops his specimens and races back to warn Jack.

A stick insect Stephen found inspires the disguise that wins the battle. After the victory, he mentions in passing that the Acheron's surgeon died months earlier, and that gives away the French captain's trick. Once again, Stephen doesn't get to study the Galápagos.

Paul Bettany plays Stephen in the film. In the books he's Irish-Catalan and, besides being a doctor and naturalist, works as a secret agent for British intelligence, a side the film leaves out. He and Jack meet at a concert in Minorca in 1800.