Ab initio restricted Hartree-Fock calculations were performed on the ground and excited states of Hf@C-28 and its positive and negative ions. Relativistic core potentials and symmetry-adapted functions were included in the calculations to take into account the relativistic effects of the heavy atom and to reduce the time and effort of the computation. Ionization potentials, electron affinities, and excitation energies of the systems were obtained and compared with experimental data or other theoretical values where available. The binding of Hf of C-28 is discussed in terms of the MO interaction diagram, population analysis, flow of electrons between Hf and C-28, and redistribution of electrons within C-28. These factors that affect the bonding between Hf and C-28 can also shed light on the characteristics of the bonding of endohedral complexes of fullerenes in general.