The One Ring is most likely inspired by the story of Gyges Ring in Plato's Republic. Gyges ring made its wearer invisible, allowing him to act with impunity. For Plato, it was a device to show how a person would behave free of social constraints. Gyges, on finding the ring by chance and discovering its power, proceeds to assassinate the local King, marry the Queen, and so take over the position of local Tyrant.
Unlike Tolkien's The One Ring, Gyges ring is not evil in itself. It is simply the power it grants its user, the ability to act without fear of punishment, that causes its wearer to become evil.
Tolkien elaborates on this, making it the source of evil, the power of the true Tyrant. Just as Plato explains in The Republic that there can only be one Tyrant in a City - Tyrants do not peacefully co-exist with one another - so Gandalf repeatedly ominously tells us "There is only one Lord of the Ring".
As Sunshine shows above, the Ring’s true power is to project its wearer’s desires, making it in reality just another tool, like all the Elven blades forged from fallen stars or under the hammer of Aule in the Silmarillion. It may be an esoteric understanding of The Lord of the Rings that the Ring never was evil in itself, but instead it magnified the pre-existing desires of those whose thoughts focused upon it, hence both Saruman and Denethor II are turned evil by lust for The Ring.
Or perhaps Tolkien is putting forward the idea that all material objects humans turn into tools are made for a purpose – and so desire in themselves to be used. Knives are made to stab people. Guns wish to shoot people. All the nuclear weapons in the world do not just sit idly. They are constantly exerting a pull on all politicians minds, awake or asleep, ‘use me’, ‘fire me’, ‘destroy your enemies’, ‘the world shall be yours’. Hmmm…. Sleeping comfortably?
So power itself is a drug which changes the way people behave, not randomly, but according to the source that gives them power. Hence Plato believed the rule of any tyrant who comes to power through the sword will be of the lowest character, dominated by their basest desires, so in fact Gyges could look forward to the least happy life of all. Plato believed his Philosopher-Kings, who come to power through their love of wisdom, would therefore rule with wisdom, and create the happiest possible state. If only Viggo Mortensen was destined to become ruler of the world instead of Arnold Schwarzenegger.