Take ownership of entire drive?

I remember there was some commandline tool icals or something

CACLS.exe

More info here:

Display or modify Access Control Lists (ACLs) for files and folders.

I think you're looking for icacls.exe.

You can also use the older cacls.exe, but watch out. cacls /G will overwrite the entire ACL by default, which never seems to be what I want, so you have to pass /E to "edit" the ACL. On icacls /grant the behavior is reversed: edit by default, pass :r to replace the entire ACL.

icacls also supports setting the object/container inherit flags (cacls does not), but you probably don't care about that right now.