Who was the captain of the German u boat?

The captain of the German U-boat is not specified in your question, as there were many U-boats and numerous captains throughout World War I and World War II. A notable figure is Captain Otto Kretschmer, who commanded U-99 and became one of the most successful U-boat commanders in history. If you have a specific U-boat or time period in mind, please clarify for a more precise answer.