Using his dad's sword Narsil, Isildur successfully cut off Sauron's ring finger ("Now I'll never be able to married!"). Because most of Sauron's evilnicity was in the ring, he promptly exploded.
Isildur was supposed to cast the Ring into the fiery chasm from whence it came, or in other words lob it into a Crack of Doom. But the hearts of men are easily corrupted and yes we are the crappest race to ever live, but you don't have to rub it in Mr Tolkien. So he kept the evil One Ring and was riding through an evil forest with it round his neck...
...when he was ambushed by some orcs who shot him full of arrows as he tried to escape by swimming downriver. The ring fell off his finger and sank to the bottom somehow.
For a long time the ring stayed there but then Gollum found it (yes, Déagol found it and then Sméagol killed him and stole it, but all this explanation just lengthens the story and then you won't want to read it). The evil Ring made him live really long until it somehow jumped away from him and a hobbit (about waist-high, hairy feet) called Bilbo Baggins found it in Gollum's cave.
Page 2 - find out what happens to the evil Ring
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