From D&D Wiki
Cavaliers are exceptional mounted combatants who take advantage of their heightened position and maneuverability to take control of the battle. http://vignette3.wikia.nocookie.net/dungeonsdragons/images/6/64/Cavalier.jpg/revision/latest?cb=20140731213132
A young, fearless halfling charges into towards the oncoming hord of hobgoblins atop his riding mastiff, swinging his longsword above his head. As the first hobgoblin raises his shield, the halfling uses his momentum to sweep his foe off its feet with his blade, already preparing to strike his next victim.
Shouting above the clashing and screaming, a female human issues commands to her comrades as she sweeps the battlefield with her strategic gaze from the saddle of her armored warhorse, already spurring her mount into action and drawing her lance to aid them in the fight.
Leaping over the mossy log, a wood-elf crouched over his wolf draws an arrow from his quiver and nocks it onto his shortbow, taking aim at the nearest warg running alongside him in the forest. Falling into rhythm with his mounts bounds, he exhales and releases the arrow with expert timing. The projectile seems to hang in the air far in front of his target before it falls lethally right between the warg's shoulders, sending the goblin rider crashing into the ground.
Cavaliers are superior warriors who dominate the battlefield from atop their steed.