Subgroups of the unitriangular group

In this article we shall construct the subgroups, normal subgroups and characteristic subgroups of unitriangular groups over associative rings. We obtain new connections between the structure of the unitriangular group $UT(n,K)$ and that of the nilpotent ring $NT(n,K)$, whose adjoint group is isomorphic to the unitriangular group.