The person operating a piece of software

For a piece of software, I am in need of a term, but being non-native English speaker, I find it hard:

In the software, a person is represented as "a member (of a community)". One such member drives, or operates the software and causes (triggers) events. Those events now need a reference to "the member that triggered the event".

What would that person or member be called?

The most descriptive terms that I come up with are all clumsy, seem to miss the point, or are "in use" already:

• "current member" – What is current? When is current?
• "operating member" – Operating gives me the idea of a surgeon operating a patient, or a driver operating a car, but not a person clicking around in a piece of software. Is that just me?
• Triggerer – is that even a word?
• "user" – Common in software, but this term is already taken due to external constraints: a user means something different already.

To clarify the last: When I am "using a website" or "using an app" (or web application), I am "the user". But from the point of view of that web application, there are many users. E.g. Stackexchange (SE) has millions of users. So, when John "upvotes" something on SE, what is that particular user called? The "upvoter" is most specific, in this example. But would there be a more generic term for "the person causing the upvote to happen"?

Since it is used in software to name methods and classes, it is hard to give a sentence, but I’ll try. I’m looking for the generic term that can replace all the specific names.

The form is "The [actor] that [caused this action], was the … ([specific name]).

• The person that made this specific edit, was the … (editor)
• The members that invited another member, was the … (inviter)
• The admin that locked this thread, was the … (moderator)
• The user that asked this question, was the … (inquisitor)

I’d prefer a single concise term and not something combined like "acting member" if avoidable.