Let k be an algebraically closed field of characteristic 2, and let W be the
ring of infinite Witt vectors over k. Suppose G is a finite group, and B is a
block of kG with dihedral defect group D which is Morita equivalent to the
principal 2-modular block of a finite simple group. We determine the universal
deformation ring R(G,V) for every kG-module V which belongs to B and has stable
endomorphism ring k. It follows that R(G,V) is always isomorphic to a
subquotient ring of WD. Moreover, we obtain an infinite series of examples of
universal deformation rings which are not complete intersections.Comment: 37 pages, 13 figures. Changed introduction, updated reference