When Isildur sliced the finger right off Sauron's hand and took the Ring, he chucked the finger in a heap of garbage, and he would never see it again. But that is only half of the story. The finger, when it was sliced off, was actually imbued with magical powers as Isildur slipped off the Ring, it being the last part of Sauron to touch the Ring. Such are the strange and varied laws of magic and supernatural abilities. Anyways, the Ring became alive, and it crawled from the heap of garbage where Isildur left it. In fact, it traveled all the way into the furthest reaches of Middle-Earth.
After years of travel the Finger made itself known to the peoples of the East. The king of one eastern kingdom hailed the Finger as a deity, and established the Cult of the One Finger to Rule Them All (the king gave himself the honor of being high priest). Thousands of pilgrims poured into the king's city each week to pay homage to the mighty Finger. Some historians say that the Finger was actually ruling the country, but they have not been able to back up their statements with firm proof. Whether or not the Finger was king, it lived its days in luxury at the Grand Royal Holy Temple of the Finger.
But when Alatar and Pallando wandered into the East some hundreds of years later, the Finger's life of luxury was interrupted. The two Blue Wizards, after visiting the Grand Royal Holy Temple, decided that to become truly powerful, they should found their own religion. They wandered into the empire just to the north, and at the emperor's birthday banquet, they burst into the hall and declared themselves prophets of the god Sûdökú. They put on a display of colorful pyrotechnics to prove their power. At this, the emperor is said to have fallen upon his knees and to have surrendered to the power of Sûdökú. Alatar and Pallando became high priests and oracles of their new religion. Their first official statement was that all Fingerians were the enemies of the Sûdökú-ites, and that a war should be waged for the great Sûdökú against the false god of the Fingerians.
And so it was that the southern Fingerian kingdom led by the One Finger was attacked by the northern Sûdökú-ite empire led by the Blue Wizards (or Highest Grand Viziers of the Great Religion of Sûdökú, as the two were now called). For hundreds of years these two nations wrestled each other, one in the name of a finger, the other in the name of a deified number-puzzle. For 800 years the two countries were at a stalemate. It was in the year 1850 of the Third Age that the northern empire released its secret weapon the Krôs-wùrd and the southern kingdom's defenses began to fail. Huge numbers of Fingerians fled the nation and headed west. They were the Wainriders who attacked Gondor. Their shields are said to have borne an image of the One Finger, and on Gondor's battlefields they would raise their shields, challenging the Gondorians to fight. Ever since the days of that war, it has been a grave insult in Gondor to give somebody "the One Finger". *
But the One Finger's kingdom recovered from the Krôs-wùrd's blows when Sauron, regaining strength, supplied his severed appendage with orc regiments. The war was at a stalemate once more. Things were looking desperate for the northern empire. The One Finger was hard to deal with alone, but with Sauron backing him, he was unstoppable. So the Blue Wizards bided their time until Sauron's back was turned, and then they struck with all their might.
It was during the War of the Ring that the Sûdökú-ites attacked. In the winter of 3018 of the Third Age they marched an army a half-million strong straight into the southern kingdom's capital. They stormed the Grand Royal Holy Temple and slew the priests and toppled the Finger-idols and carved great Sûdökú grids in their places. But they could not find the One Finger. In fact, it was taken by a Sûdökú-ite foot soldier who had came across the finger in the midst of battle and took it as a souvenir, thinking it was an ordinary finger cut off in the fighting. The solder ended up carrying the One Finger for the next three months.
In March the soldier was sent to the western front in Sauron's war against Gondor. He was taken prisoner by the Gondorians at Pelennor. When he was interrogated, the Gondorians discovered this finger in the man's pocket. The interrogators informed their superior officer, who demanded the finger be gotten rid of and forgotten. It is not known whether he knew of the finger's true nature or, if he did, if he informed the Steward. The One Finger was locked in a tiny box and put into storage, where it still rests today millennia later, plotting its return.
As it turns out, the Blue Wizards actually succeeded in their mission against Sauron when they destroyed the One Finger's kingdom. If it were not for them, Sauron's finger would still be worshipped as a god today.
* Idea "borrowed" from Fordim. I just couldn't resist.
