Coffin was a member of Laughing Jack's crew on his ship the The Lady Luck who led a mutiny against Jack. He was the only crewmember to be spared from the curse of The Lady Luck.
Under orders from the Shadow Lord, Laughing Jack instructed his crew to sail The Lady Luck to Bone Point so they could put out the lighthouse. Jack attempted to do this by indenting the keeper of the light, Red Han, but when that plan failed he kidnapped Red Han's daughter, Verity. The moment Verity came onto the ship, all wind vanished from Bone Point, stranding The Lady Luck. This caused Coffin to believe that the sea had cured them for taking Verity aboard. His beliefs spread among the crew members when seabirds arrived to give Verity food and water, despite the crew of The Lady Luck to keep them away.
On the day of the Shadow Lord's invasion, Coffin lead a mutiny against Laughing Jack with the intention of freeing Verity and letting the ship sail away from Bone Point. Jack told them that they could leave now, since the Shadow Lord had no further need of the lighthouse, but when he ordered his crew to the ship's oars, they refused to move. Jack was able to convince them, however, by promising them all the gold in his current possession if they manned the oars until new replacements could be found. Coffin spoke out against this, saying that Jack was trying to trick them like he tricks everyone. For this, he was stabbed in the back by another crewmember named Beef.
Coffin's lifeless body was left on the deck of The Lady Luck when the rest of the crew went below deck. It later rolled into the sea when Jack killed Verity and brought the wrath of the ocean upon his ship.
The Isle of the Dead
Lief and Barda saw Coffin through Verity's painting when they became stranded on The Lady Luck.
Coffin was superstitious and fearful of strange and unnatural occurrences, and believed that the land and sea could become angry with humans. Among his crew mates on The Lady Luck, Coffin was the only one not fueled entirely by greed, as he refused Laughing Jack's offer to row The Lady Luck for gold and urged his crew mates not to accept. He was also reasonably smart, realising that Laughing Jack's offer would most likely be a lie to save himself.
Coffin was an experienced sailor because he served on The Lady Luck for a reasonable amount of time.