Death/the Conqueror Worm
You really can't talk about these two separately: they call out to each other; their conflict can be found right there in the beginning: "Man doth not yield himself to the angels, nor unto death utterly, save only through the weakness of his feeble will" (1). There you have it, main attraction: man's will vs. death. As far as we know, the will of man has never won out. Ligeia's own poem, "The Conqueror Worm," suggests that it's a losing battle, but at the same time she asks God "shall this Conqueror be not once conquered?" (16). At story's end, we know that it has finally been conquered, and that the one to finally triumph over death is none other than Ligeia.