What is the name for the person who explorer under the sea?

A person who explores under the sea is commonly referred to as an "underwater explorer" or "marine explorer." In more specialized contexts, they may also be called a "diver," particularly if they are using Scuba gear, or an "oceanographer" if their exploration is scientific in nature. Additionally, those who operate submersibles or underwater vehicles may be known as "submersible pilots" or "submersible operators."