And I may not be able to list of all them for you advanced users. But for our Jr. BA or those who have very little experience gathering user requirements, these are the folks that you should consider when planning for the collection of user requirements:

"Mud on the boot" users: these are the front line users. They will be using your product on a daily basis. A frustrated "mud on the boot" user can be like a virus. They like to vent or complain about their products. They will tell you how they do their jobs, and how they would like to see things improved. They may also have some level of competition among each other so if your product allows them to perform their activity efficiently, they will rave about it.

The "Wind Stoppers": they perform the middle man role. They deal with the "mud on the boot" users on the daily basis and know the pains and successes of those users. They provide assistance, run reports, and overall understand to some degree the needs of the the "mud on the boot" users. If your organization sells directly to the "mud on the boot" population, your "wind stoppers" will be internally, such as customer service, call center, sales department, training department... etc.

and finally the "Fixer Uppers": if anyone can give you what the users have difficulties with, the "fixer upper" is the person to talk to. Once the "wind stoppers" intercept the issues on the field, the "fixer uppers" are deployed to patch things up and allow the "mud on the boot" users to smile again. They understand the error paths, they will give you alternate scenarios (we will talk about this later). These users can be found in your field service agents, technical support department... etc.

If you know of some other user group that I missed to get "user requirements, I would like to hear from you...

Your next step is found in Gathering User Requirements - Part 3: Know Thy Users