  Let O be a complete discrete valuation ring with finite residue field k of
odd characteristic. Let G be a general or special linear group or a unitary
group defined over O and let $\mathfrak{g}$ denote its Lie algebra. For every
positive integer l, let $K^l$ be the l-th principal congruence subgroup of
G(O). A continuous irreducible representation of G(O) is called regular of
level l if it is trivial on $K^{l+1}$ and its restriction to $K^l/K^{l+1}
\simeq \mathfrak{g}(k)$ consists of characters with G(k)-stabiliser of minimal
dimension. In this paper we construct the regular characters of G(O), compute
their degrees and show that the latter satisfy Ennola duality. We give explicit
uniform formulae for the regular part of the representation zeta functions of
these groups.
