  The topological charge of a maximally symmetric black hole naturally arises
in holography, which can be viewed as the last charge of the black hole in the
sense that it together with all other known charges satisfies the holographic
Gibbs-Duhem-like relation as a completeness relation. It is then observed that
this topological charge, which we have missed before, fits perfectly into the
black hole thermodynamics from two different approaches, not only in Einstein's
gravity, but also in the general Lovelock-Maxwell theory.
