In the book Robur the Conqueror Robur makes a challenging speech at the Weldon Institute of Philadelphia, a club for the supporters of lighter-than-air craft (balloons) and tells them loudly about the benefits of heavier-than-air flying vessels, successfully spawning trouble and chaos. That very night he kidnaps the president and secretary of the Institute, Uncle Prudent and Phillip Evans, as well as Prudent's valet; and makes them all prisoners in his odd, powerful vessel. Throughout the novel, Robur travels around the planet in the Albatross and not only refuses to release his hostages but also refuses to reveal any clear information as to where they're going and what is the purpose of their capture.
After a huge hurricane, the damaged Albatross stops by a small Pacific island and the hostages see chances of escape at least; angered by the several months of captiveness, albeit with comfort and nice treatment, they decide to place a bomb in the Albatross, successfully destroying the vessel after their escaping and apparently killing Robur and his crew. Near the end of the book, however, as Prudent and Evans are making the first flight of their mighty balloon, the Go-Ahead; Robur shows up alive and with a newly repaired Albatross seemingly to seek vengeance. Still, when the balloon accidentally bursts, Robur rescues and releases his ex-prisoners instead of capturing them again; also making another speech to the public where he acknowledges that the world is not yet ready for his invention. After this he departures.
Despite his arrogance, Robur performs at least three actions in the novel which can certainly be considered heroic, or at least noble: the first is when he shots alarming bombs at an African tribe in order to allow those who were about to be sacrificed to escape. The second is when he rescues a group of castaways in the South Pacific, giving them fresh water and food. And the third is the afore-mentioned occasion where he rescues those who had destroyed his old ship and attempted to kill him. Overall, in the original novel Robur can be considered more of an eccentric, ambiguous figure than an actual villain; somewhat akin to Captain Nemo from Verne's 20,000 Miles Under the Sea
In the sequel, Master of the World, published in 1904, Robur is played out as more villainous and is able to built a craft even more impressing than the Albatross: the Terror can move through both air and water and is able to reach such tremendous speed as to become invisible to the naked eye.
The movie, Master of the World, is based on both the original novel and its sequel. Robur is played by Vincent Price and is this time an obvious villain; specifically a coup d'é tat who wants to use the Albatross to attack the world's major cities in order to replace the current governments with a pacifist dictatorship with him as the ultimate leader. According to him, this should put an end to all war and misery and create a better world.