Yes the name is from Israel and last name is Cohen. So why he use A. Before Cohen?You won't get a good answer without a context. Is it a name of a real/fictional person? Is it a name of an Israeli? Secular/religious? Most Israelis don't have a middle name but when that do, it's definately NOT a tribal or ethnic indicator.
Last names can be tribal or ethnic indicators, for example Ashkenazi or Cohen.
Because his middle name starts with A. Simple as that. His full name could be Ronen Adi Cohen, or Ronen Aaron Cohen, or Ronen Asher Cohen, or... Just like George Walker bush is abbreviated George W. Bush.So why he use A. Before Cohen?