User Not Visible in AD Users and Computer

I don't agree with the given answer.

You are allowed to create user accounts that end in the dollar sign ($) character, and Active Directory can still tell the difference between that user account and a computer account, because the object still has user as its ObjectClass.

I just created a user with a trailing dollar sign in the name, and there were no issues viewing the user account in ADUC, or Powershell, or the ADUC search dialog. The account was just fine.

So your problem lies elsewhere.

So my theory is that someone has changed the showInAdvancedViewOnly attribute on that user account to TRUE, and this will hide the user account from the ADUC console's view, unless you were to check "View -> Advanced Features" from the menu.

Not 100% certain, but that's my bet.

Edit: It's also worth noting that creating a user account with a trailing dollar sign, while technically legal, is not something that you just "accidentally" do. For instance, ADUC would not allow me to do it. It just silently stripped the dollar sign. However, using more advanced methods, I was able to get the dollar sign onto the end of the CN of the username. So all things considered, this sounds a little fishy, like someone trying to hide a user account.

It looks like an account that gets created when you have an AD trust setup. You should be able to see it in ADSIEDIT. Look at the extended properties for sAMAccountType (TRUST_ACCOUNT). The account name will match the domain name that the trust is setup with.