All throughout fiction and creative non-fiction you are going to see fully realized characters with qualities and self-contained facts that are unique to them. This translates to their background, mannerisms, even the more static things like their name and occupation. It is also likely, though less so, to find many characters that have or go by more than one name. This can be a number of things in life, such as a professional title, legal name, and nickname. In a screenplay this has even more precedence as you may want to even withhold a proper name for a period of time and first introduce them using a description as a title marker. There is a specific way to format this multiple name paradigm when you are writing your screenplay.