not allowing to su

I know that in freebsd you have to allow a user to be able to su to
root. I just installed debian on a machine and want to be able to do the
same thing.
To allow a user to su you have to add them to the wheel group in freebsd
if my memory serves me correctly, but I don't see anything like that
here in debian.

Can someone help, I only want one user to be able to su to root and
nobody else , and I want to use linux :)

Thanks in advance,

Donald