Becouse Hecarim is pro in the jungle. He levels fast and he has a perfect gank-ult. These ult is also perfect for multi kills. And kill someone behind a turret. All those things you will see later in this guide.

I've chosen the Quintessences of swiftness cause of his passive, how bigger de movement bonus how bigger hecarim's attack dammage bonus. And if you're fast you can escape very easy. So one Quintessence bonus two during game bonusses.
Than we have the Marks, I've chosen the mark of strength because the marks give the most strength bonus and a bit more dammage is very important for low lvl ganks.
the Seals and Glyphs give bonus attack speed, that's very important with jungling.

The masteries give armour penetration, attack speed and damage. That's just chil in jungle and in team fights. And you have an advantage in early game ganks.

Begin items Boots and 3 health potions, because the boots are with hecarim's passive also attack damage. And it's chil to be fast. I've bought the health potions because you can survive longer in jungle.

Early game items Wriggle's latern, ninja tabi, phantom dancer and two sigt wards. Wriggle's latern because then you can stay very long in jungle by lifesteal and the 20% chance to hit bonus dammage on minions. ninja tabi because the chance to dodge and the extra movement speed (also dammage for hecarim). Phantom dancer because if you have phantom dancer it wil give you extra movement speed(also dammage for hecarim), and much attack speed, so you can stay forever in jungle with full hp, the critical hit is also chil but extra chil with infinity edge. Sigt wards, you have to place them one nearly the baron and one nearly their blue buff. The dragon sigt is good for two reasons, 1 you can steal the dragon easy, with ult. 2 you can take out their team by going with your team to the dragon and just kill everybody.
Late game items Infinity edge, another phantom dancer and Madred's Bloodrazor. Infinity edge because the critical hit bonus and the extra dammage, if you have infinity edge your basic attack will be very much stronger. And because you've bought a phantom dancer already, you have a good chance for critical. The second phantom dancer allowes you to run away very easy and when some of their turrets are destroyed and when they push you can kill them. It also gives the perfect critical so you're now OP. And the finishing touch, Maldred's bloodrazor, I've chosen it because it grants you the possobilitie to kill a tank easy, more attack speed and more dammage, if you have all of these things, you're officialy OP!

You have to level W first, it's very nice in team fights and you have more survivalbillity. Then Q because it's going to do much dammage in combination with R. And last lvl E because it has only a big status effect so if you have it lvl 1 you can do nearly the same, excluding dammage.

Smite is clear of course, because you're jungling. You can't kill a buff at lvl 1 whithout smite. And I've chosen ghost because it grants extra movement speed, so extra dammage, and you can escape faster.

You have to make hecarim very fast and strong, so you're the perfect assasin.

Pros:
-Very good jungler
-Nice ganks with his ult
-Good in team fights with ult and Q
-Good looking

Cons:
-Low dammage early game
-Low health early game
-Q low dammage early game