I would refer to someone I used to work with as a former colleague or a past coworker. Depending on our relationship, I might also call them a friend or mentor if we had a closer connection. The specific term would depend on the nature of our work relationship and the context in which I am mentioning them.
That would be a derivative work, which requires a license from the rightsholder of the original work.
Copying someone else's work without permission is called plagiarism.
Employee
It means to employ someone.
Slavery
Such a person could be called: Work Shy. Or sluggard
Plagiarism is the term used when you copy someone's work without giving them credit.
Tenant
It is called plagiarism.
Taking someone else's work as your own is called plagiarism.
associates, co-worker, acquaintances
metallurgist