In UML use cases, someone or something who interfaces with your system to do work is an "actor". This actor can be a human or another machine or piece of software (many programs launch other pieces of software either with specific predefined goals or to take control of them with scripts or other automation).

From a more business-related perspective, if your software is used primarily or exclusively by people who work for or have a business relationship with the company that will "own" your software, you might consider using the person's job description or other business role (such as "customer" or "visitor"). There are as many euphemisms (and dysphemisms) for "worker" as there are companies, so this may be confusing if your terminology will be exposed to people outside the corporate culture, but "CSR" (customer service representative - the generic term for the human user of a CRM software package) and other relatively neutral terms are usually fine to have in software documentation, provided there is a footnote somewhere defining the term.