The rogue is not concerned with the "virtues" of knighthood, nobility, or morality. The rogue serves no one but themselves. Rogues are masters of deception, theft, and the effective but honorless ability to stab others in the back.
These fellows are not disciplined like soldiers, but they tend to be very quick, often eluding more powerful foes and are quick to relieve the general populace of their heavy coins and possessions. These untrustworthy souls utilize their knowledge of the city to evaluate and steal items of great value, fence them at great profit, surprise their enemies or 'marks,' and evade their antagonists with great alacrity.
The prime requisite of rogues is dexterity which makes them very slippery opponents. Strength is desirable to make their primary attack, the backstab, more powerful and to allow them to carry more loot. Intelligence is a big plus, allowing them to learn their skills quickly and expertly as well as to assist their streetsmarts. And as with all classes, a hardy constitution will help them survive in the lethal dark alleyways and sidestreets of the big cities.