Muhammad

هذا الاسم هو الاسم الأكثر شيوعًا في العالم حيث أطلق عليه مائة وخمسون مليون شخص.
[This name is the most common name in the world with one hundred and fifty million people using it.]

8th most common boy's name in England and Wales.

It's used in Saudi Arabia to address a person whose name someone doesn't know. "By the best of names". Though I think partly also because it's so common increasing the chances of a correct assumption.

Used by Muslims. Non-Muslims don't use this name or the names that derive from it. The Prophet Mohammad (peace be upon him) was sent to all mankind as the seal of all prophets.