In the Genesis account, God shut the door of Noah’s Ark. Genesis 7:16 says that Noah, his family, and the animals entered as commanded, and then the Lord shut the door behind them.
This detail appears immediately before the Flood waters rise over the earth. The passage distinguishes between Noah’s role in following the instructions and God’s action in closing the Ark, giving the moment a clear theological emphasis in the narrative.
A common mix-up is to answer Noah because he is the Ark’s builder and organizer. Genesis does describe Noah constructing the vessel and bringing the animals aboard, but the text specifically assigns the final closing of the door to God.
The account does not say that an angel closed the entrance, nor does it describe a mechanical locking system. Later paintings, children’s books, and films may dramatize the scene, but the biblical wording identifies God as the one who shut the door.