Alberich's Curse

In his rage over the loss of his Ring, Alberich puts a curse on the Ring that, until it returns to his possession, it shall give no power to anyone. Rather, it would make whoever does not have the Ring to covet it, which in turn would cause any present owner of it to be consumed by fear of losing it, thereby deriving no value from it, and eventualy dying by it.

Alberich performs this curse when the ring made from the Rhinegold he stole from the Rhinemaidens is taken from him by the Gods Wotan and Loge to pay the Giants Fafner and Fasolt for building Valhalla. The first victim is Fasolt, slain by his brother Fafner as they argue over the ring. Fafner himself becomes victim to the curse, as he is reduced to hiding in a cave for fear of heroes wanting to claim the Ring, and is indeed eventually slain by Siegfried. Alberich himself notes that Siegfried is unaffected by the curse (because he doesn't know it, paying no heed to Fafner's mention of it) until Hagen forces events into motion that result in Siegfried's death. Indeed, the Ring's final victim is Hagen himself, who tries to retrieve from the Rhinemaidens, who drown him.

The power of the curse is ambivalent and could be seen as purely the power of suggestion, being that all desire the Ring. Indeed, Siegfried is unaffected by it precisely because he doesn't know of it (beyond Fafner's fleeting mention of it) until the Rhinemaidens explain it to him. In fact, most of the aspects of the curse as described by Alberich already apply to himself before he invokes the curse, with the Dwarf being so preoccupied with the possibility of losing the Ring that he commissions the creation of the Tarnhelm and is ultimately destined to lose it to Wotan.