Hadras was a crewmember serving aboard the Flying Dutchman. He is one of 6 senary antagonists in Dead Man's Chest and a minor antagonist in At World's End.
He served as a crew member aboard the Flying Dutchman under the command of Davy Jones. As with other members of the crew, Hadras had, over time, taken on aspects of the sea flora and fauna the crew resided amongst. He spoke Cantonese, possibly indicating his place of birth. Hadras's body was covered with coral and barnacles, though most notably was the fact that his head was ensconsed within a conch shell. More, his head had in fact transformed and merged into a hermit crab that could move independently of his body, propelled by a number of small, crab-like legs.
During "Dead Man's Chest"
During the fight for the Dead Man's Chest on Isla Cruces, Hadras's head became detatched from its body thanks to a well-aimed coconut thrown by Jack Sparrow. The head was forced to shout directions as Hadras's body blundered about blindly trying to relocate it. He managed to pick up his head, and carried it under one arm. Hadras later confronted James Norrington, in possession of the chest, who, in an act of apparent cowardice, threw the chest into Hadras's arms and fled. However, this meant the pirate was forced to drop his head to catch the chest, and his body forgot to retrieve it when the rest of the crew arrived. Hadras's body raced with its fellow crewmen back to the Flying Dutchman, with his disembodied head scuttling after, desperately trying to catch up. During the battle around Calypso's maelstrom, the Dead Man's Chest landed on Hadras' head, pushing it into his torso and sending him toppling overboard to his death.
After Davy Jones was killed, he along with other crewmembers returned to their human form.