Octesian

Lord Octesian was one of the Seven Lost Lords and a Telmarine lord who opposed King Miraz. These lords did not fear the oceans or forests, unlike most telmarines, and were of the few respecting the legends of Old Narnia, or Narnia before the invasion from Telmar.

Biography
Octesian and six other lords were sent to "explore the seas beyond the Lone Islands" by King Miraz in an attempt to get rid of them. Lord Octesian is presumed to have died on Dragon Island, for this is where his Lord's bracelet was found, along with his assets and treasures.

When the Dawn Treader disembarked on Dragon Island, Eustace Scrubb explored it. During his exploration, he saw a dragon dying, and a load of treasure, including the bracelet of Lord Octesian himself.

Because of this, it is unknown whether Octesian was killed by that dragon, or if he was actually turned into that dragon himself, unable to resist the temptation to steal the island's great treasure (the same temptation that later turned Eustace into a dragon). If the latter assumption was true, then Lord Octesian died as a dragon, and shortly afterwards was eaten by the dragon version of Eustace.

Arm Ring
As he belonged to a great Narnian House, Octesian wore an arm-ring bracelet with the crest of his family engraved on it, a hammer under a star. After it was found, everyone had to assume that he was dead, so the bracelet was hung upon the cliff of the bay of Dragon Island, with the following inscription engraved upon the cliff: -

'DRAGON ISLAND DISCOVERED BY CASPIAN X, KING OF NARNIA, ETC. IN THE FOURTH YEAR OF HIS REIGN. HERE, AS WE SUPPOSE, THE LORD OCTESIAN, HAD HIS DEATH.'

Film Version
In the 2010 film version, Lord Octesian had fled to the Lone Islands to escape Miraz, along with his 6 fellow Lords. Once there, they learned of the Green Mist that was abducting people. They all swore a pact to find the source of the Mist, and destroy it.

Octesian made it as far as Dragon Island, which coincidentally was also Deathwater Island, where he and Lord Restimar died. Eventually, his remains were found by Eustace who had been exploring the island, and who then stole his arm-ring, which in turn cursed him into a dragon.

Eustace was the only dragon on the island, and Octesian's human bones had been found, so he had definitely not been turned into a dragon. Though whether he had been killed by another dragon that used to live there, or simply died from thirst/hunger, is another story altogether.

Trivia

 * In the book, Eustace couldn't get the bracelet off him, and it caused him great pain. But in the film, Lucy pulled it off him.