Final answer:
Dad's Key is the item in the game 'The Binding of Isaac' that unlocks all closed doors in the current room and can open the golden door in the Dark Room or the Chest.
Step-by-step explanation:
The item in the game 'The Binding of Isaac' that unlocks all closed doors in the current room, including those requiring keys to enter and secret room doors, and can open the golden door in the Dark Room or the Chest is Dad's Key. This item is a consumable and can only be used once per room. It is a valuable tool for exploring and accessing various areas within the game.