When the game begins, Dust awakes in a forest with no memory of who he is, where he is, or what he should be doing. The only clues he has are a talking sword called The Blade of Ahrah and an odd flying critter named Fidget who is charged with looking after the aforementioned sword. Together the three embark on a quest to discover Dust's true identity and save the world.
Dust is a skilled swordsman who can do everything from parry enemy blows (which stuns them) to launching them into the air for air combos. Early in the game he learns a skill called Dust Storm. This involves spinning Ahrah around at extremely fast speeds. So fast, in fact, that if it is held for too long, Dust begins to turn red and hurts himself. But when done correctly, the move can do massive damage to enemies, and power up Fidget's magic attacks. And, as an added bonus, it sucks up nearby items and money dropped from enemies and chests. If Dust does it in the air, he spirals horizontally through the air (though he does eventually dip down), and it retains the same effects as on the ground.
While Dust is focused on his quest to learn his true identity, he is good-natured and kind enough to help out any person in need (often in the form of side quests). He'll even give out autographs, if asked. Generally speaking though, he is very humble and modest, despite being able to slaughter his way through thousands of monsters. But that modesty doesn't stop him from poking fun at Fidget's goofiness.
Dust's origin (End Game SPOILERS).
Near the end of the game it is revealed that Dust is not actually amnesiac, as he has no true memories to recall. In reality, he is actually the Sen-Mithrarin, a being created artificially through the magical combination of two souls. Elder Gray Eyes, the leader of the Moonbloods (lizard people) combined the souls of Cassius, an assassin who worked with General Gaius (the game's villain), and Jin, an innocent young man. Jin and Cassius killed each other at the same time, and Gray Eyes believed (correctly) that the combination of Jin's pure heart and Cassius's combat skill would be what was needed to defeat Gaius and his army. However, despite the fact that Dust has two souls within him, his personality is separate and distinct from those of either of the souls in him, and he initially remembers nothing from the life of either (not counting how to kill thousands of monsters). He is neither Jin nor Cassius, he is simply Dust, and the moment the player begins the game is actually the moment his life begins.