Wodan + Tiwaz = Odin
At the time of Tacitus however there is reason to believe that the Roman god of war, Mars, was identified not with Wodan, but with another Germanic god, Tîwaz. Odin in fact appears to be the successor of both Wodan and Tîwaz, retaining some of the qualities and attributes of both these gods.
H.R. Ellis Davidson in Gods and Myths of Northern Europe (1964)