Alexander DuBrow is the main antagonist in the Goosebumps book Deep Trouble. He is a science assistant to Dr. Deep and is the custodian of his boat and equipment. He is somewhat obnoxious but is not a full villain until halfway through the story.
When Dr. Deep and his niece Sheena and nephew Billy are studying marine wildlife, Billy has encounters with a giant squid which Dr Deep laughs off, and then Billy for real comes into contact with the mermaid said to haunt the place. He brings her with him but Alexander captures her. They all study her but she is calling for her other mermaids. Alexander knows the mermaid is in distress but doesn't want her freed for financial matters. Later, Billy notices some men on a boat coming to their ship at night. They kidnap the mermaid.
Billy runs up to them and tries to fight them off but they knock him to the floor. Then Alexander comes in. Billy wants to see Alexander punch them out because he is strong, but then to his dismay Alexander sides with the men, revealing he was their leader all along and planned this kidnap. He betrays Dr. Deep and the others by throwing them in the mermaid tank, locking it, then throwing them overboard to drown.
But the mermaids come and save them, then they head to Alexander's boat. Alexander and his thugs come out and try and fight them, setting their boat on fire. But the mermaids come and rock the thieves' boat back and forth.
Alexander is never seen again in the book; it is unknown if he or any other members of his crew survived the mermaids' attack.