I drift forever with the current down these long canals they've made. Tame, yet wild, I run elusive, multitasking to your aid. Before I came the world was a darker place. Colder, sometimes, rougher true. But though I might make living easy, I'm good at killing too.
What am I?
This was Gollum's final riddle from The Hobbit:
"This thing all things devours;
Bird, beasts, trees, flowers;
Gnaws iron, bites steel;
Grinds hard stones to meal;
Slay king, ruins town,
and beats a mountain down."