Dr. Bellrog is one of the ghosts residing on Raven's Cove in El Patron's Mine. At one time he was an explorer who had ventured to the island along with his loyal bodyguard Kudgel. However, when the battle between Jolly Roger and the Black Guard erupted, they hid in the mines - only to be killed. It is unknown the exact way that he died.
The pirate will meet him as part of the Raven's Cove Story Quests. Bellrog knows some of El Patron's history and can read older texts. He offers to help the pirate in their quest to find the Cursed Blades of El Patron.
Game Note - Contains Spoilers!
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Once the final idol is found Dr. Bellrog says the player is of no use anymore and orders Kudgel to kill the player. After defeating him, the player can go into the door to eventually challenge El Patron.