Nemo

 was the Captain of the Nautilus. He was sent to search for the Sixth Doctor in the furthest regions of the realm (AUDIO: The Wreck of the Titan)

He rescued the Doctor after torpedoes hit Long John Silver's boat. He sent the fairies, to help Jamie McCrimmon, Rob Roy MacGregor and Alice Lydell fight cyber-converted magical creatures. After bringing up the TARDIS from the sea floor, he was attacked by cyber-mermaids. He was almost converted but he along with Dracula and the Karkus attacked the Cyber-Planner. He disappeared when the Cybership blipped out of existence. (AUDIO: Legend of the Cybermen)

The Master once encountered Captain Nemo in the Land of Fiction. (COMIC: Character Assassin)

Behind the scenes
Captain Nemo is a character in the novel 20,000 Leagues Under the Sea.