Within the context of the Wedderburn-Malcev theorem a radical complement
exists and all complements are conjugated. The main topics of this work
are to analyze the Determination of a (all) radical complements, the
representation of an element as the sum of a nilpotent and fully
separable element and the compatibility of the Wedderburn-Malcev theorem
with derived structures. Answers are presented in details for
commutative and solvable associative algebras. Within the analysis the
set of fully-separable elements and the generalized Jordan decomposition
are of special interest. We provide examples based on generalized
quaternion algebras, group algebras and algebras of traingular matrices
over a field. The results (and also the theorem of Wedderburn-Malcev and
Taft) are transferred to non-unitary algebras by using the
star-composition and the adjunction of an unit. Within the App endix we
present proofs for the Wedderburn-Malcev theorem for unitary algebras,
for Taft's theorem on G-invariant radical complements for unitary
algebras and for a theorem of Bauer concerning solvable unit groups of
associative algebras.