Hecarim is a strong jungler, with some pretty nifty perks and tools. His kit is perfect for ganking and doing some vicious 1v1. His Q makes him clear the jungle really fast and some really clean counter jungling. He can easily turn matches around with his incredible ganking and burst dmg capabilities. Overall his scaling makes devastating if left to his own or even fed.

The masteries for Hecarim work really well to jungle at max speeds while keeping his ganking potential high. I take the Summoner's Wrath and Summoner's Resolve for two things

Ghost makes you move faster, more movement speed ,more dmg. More dmg equals more kills, more kills means win
Smite give you 10 gold on use, meaning insuring your dragons and buffs give you EVEN more money and is a nice extra source of income that adds up

I take AD,AS,and Arm pen so that i deal more damage and the extra 10 arm pen is worth it. In utility my main focus is to get the movement speed and the rune buffs. With the movement speed gives you a hefty amount of extra ad because it begins to scale with the higher movement speeds. Also increased buff time? Yes please! Blue buff is vital before your sheen and helps your CD greatly so your can Q more. Also red buff works well so you can stay in Rampage range while also dealing dot dmg that can ensure kills.
In the defensive tree I take the reduced dmg from monsters to increase my time in the jungle. I get the armor and health trying to reduce the amount of dmg to help mitigate the squishyness he tends to have.
I take the Bladed Armor , Indomitable , Veteran's Scars for two purposes

Bladed armor returns damage from attackers witch helps out against creeps and other attackers it helps do that much more dmg
I get scars because it helps with his health problem and will help you survive that early jungle route. Indomitable also contributes to his sustainability by taking less dmg all together

That is my prefered build as it helps me last longer in the jungle and gank lanes quickly and effectively, you can go full assault masteries and hit harder however his jungle time suffers due to the less sustainability.

His runes are Pretty basic on him, you want the Greater Mark of Desolation for the jungle creeps and champions, you want the Greater Seal of Armor for the jungle and ad carries, and the Greater Glyph of Magic Resist for the pesky mages thinking there all big and bad. And finally the Greater Quintessence of Movement Speed , now you may be thinking, why movment speed? Then you remember that his passive is awesome and are like, F**k yeah Movement speed! 4.5% increased movement speed works well because by level 18 his passive gives 22.5% of his bonus movement speed as attack damage.

I Choose Smite and Ghost as my summoner spells. Why? Because any jungler who DOESN'T use smite should not jungle. Smite helps you keep dragon and baron control, witch i have stolen plenty of times and makes your team happy (Who doesn't like a free 190/300g or free baron). It also helps insure buffs from enemy capture, such as getting your level 1 blue (see jungling section). Also you can use it to counter jungle your opponents buffs and what not. Overall its a essential jungling spell.

Ghost helps out TREMENDOUSLY because of two things.

It increases movement speed, witch if we remember gives us attack damage, and the more movement the better.
And secondly it lets you move EXTREMELY FAST. If you use with with your E(

Devastating Charge) you can insure a kill (unless they use Flash and what not, escapes)

Other Good Spells

Flash I used this for a lot of my champions and is one of THE GREATEST spells in the game. However it has no room for Hecarim so were going to have to pass, its a wonderful tool if your solo top just not for jungling.

Exhaust Its a great spell if used correctly, as i fancy in the support role, using this at crucial times can make or break team fights. For example you and your team are in mid lane trying to push inner turret and everything is running smoothly. Suddenly a wild Nunu & Willump appears and you know what hes going to, hes going to ult for incredible damage. But you got your exhaust in your pocket and you use it on him before it finishes and it avoids any deaths and hinders them greatly. This is one of the other spells that I would take for top lane just not jungling. Ghost and Smite are just better.

Teleport again good choice for top not for jungle. it helps you get where you need to be. Great spell, just not for Hecraim

Ignite This spell is really good for top lane, but alas has no place in the jungle. It insures kills and if you get Summoner's Wrath it gives you a nice boost in ap/ad.

Spells that you should not choose

Clarity I've only seen this in ARAM some people use it well , bottom line you shouldn't have mana problems please don't use it.

Heal works well with heal baiting in top lane, but again this is a jungle guide not top lane so please don't take it.

Clairvoyance Your not support, please don't.

Cleanse its a great spell, but there is an item in game that dose exactly that Quicksilver Sash so if you are facing against a heavy suppress/cc team get QSS not cleanse.

Promote -_- please, don't

Surge I like it for my cho'gath makes me eat that much more, other then that it isn't very reliable.

Revive Please leave this for the Karthus that likes to penta with his Requiem

I've noticed that frequently I have to build boots to counter a lane or the team as a whole. So seeing that I've deiced to make a boots section to help with counter other champions.
Mercury's Treads These boots i put in the main build, some people ask why? They argue that Boots of Swiftness are better because of his passive, why build t2 boots when you can get t3? Well most teams have a form of crowd control, taunts, stuns,slows you name it. Now being able to move quickly OUT of disables instead of just moving quick helps more the the extra speed. That's why i put merc treads in the build, because most teams have Crowd control.

Ninja Tabi These boots are good for Auto attack champions, such as Garen, Ashe, Graves ect. Basically any AD carry. Its very rare you see this happen, but if you just can't stand that Tryndamere.

Boots of Swiftness Only take these on the rare occasion that the enemy team has no CC, which i highly doubt, still there are times were i'll take these for me dmg.

Berserker's GreavesPlease don't take these, they are for AD carries, and other boots provide more benefits then these.

Now this is the part where your confused on what skill does what and witch scales better. Now i find it that maxing your W first is really good for jungling and surviving during a gank. But I also like putting points in Q to do the most damage in a gank. Your E is pretty meh, it increases in damage only slightly and the movement is constant throughout the ranks.

A quick little rule of thumb is to go R>W>Q>E for your skill points. Other then that its pretty straight forward.

TLDR

Onslaught of Shadows> Spirit of Dread> Rampage> Devastating Charge

I always start Boots and 3 Health Potion for early damage and helping you through the first clear. Some like to run Cloth Armour and 5 Health Potion but I will cover that in the jungling section.

I then build Wriggle's Lanternbecause of the on hit effect helps with clearing the camps. Afterwards I get a Sheen because the proc on spell use it very strong in conjunction with Rampage makes your auto attacks very destructive.

This is where I start building the pieces of Trinity Force better known as Tri-force. Tri-force's procs and stats works extremely well with Hecarim's kit. The movement speed, with the sheen proc, and the slow just makes it too good to pass up. I get a Zeal and then a Phage for the pieces of Tri-force. At this point you'll be dealing tons and i mean TONS of damage.
I personally like picking up a Wit's End despite its recent nerf. It works well with his auto attacks and helps you become that much tankier.

Finally the final items, thesse are things you can sub out depending on the team comp (such as getting QSS, Thornmail, Banshee's veil, ect.) I get a Force of Nature because of the movement speed, magic resist, and health regen. The movement gives you a nice amount of AD by the time you build it.

I get a Bloodthirster for the AD and life steal. At this point sell your lantern for the increased life steal, its been a long match, but at that point you have to say good by to your favorite lantern. My last item is the beloved Phantom Dancer the MS, AS, and crit on it makes it quite the item for Hecarim.

Other items

Maw of Malmortius Some people like it, but it doesn't match my play style, I don't like being at low health and i like to play it on the "safer" side if you were to sub this in I would take out Wit's End"Edit: I take it for solo top because the bonus ad can really turn a gank around."

Frozen Mallet I like this item because it keeps my prey slowed, however because of Trinity Force you wont need FM. If you want to take this i'd sub out Wit's end or Force of nature.

Madred's Bloodrazor this is the item you use when the like to stack health and stuff (those 5 warmog's mundo's Im looking at you! >:|) other then that i wouldn't take it. I'd replace wit's end if i were to take this.

Ok now this is the "How to" part, if your a veteran jungler you wont learn anything new. Hecarim clears the jungle really fast because of his Rampage and Spirit of Dread, making blue buff a big deal for his jungle times. The first blue is very important for him, make sure to get your team to defend your blue, because like Amumu his very mana hungry in till you get your Sheen. Your route should be Blue buff onto to wolves onto wraiths on to golems and then red buff. If you are running Boots and 3 Health Potion you should use one potion on blue buff, one at golems and one at red buff. Some people like to use the set up Cloth Armor and 5 Health Potion making it 'safer' for jungling. Warning If this is the first time your jungling and have not practiced it for a long enough time take the Cloth Armor and 5 Health Potion once you get the hang of jungling and feel you can take more risk's then start taking Boot of speed and 3 Health Potion. After your route you should Recall and grab a Vampiric Scepter you should be very close to level four so go kill wolves (they should be back) or wraiths and once you hit four go ahead and gank lane. Depending on what side your on is how you want to approach ganking. Bot lane you want to wait in Tri- bushes by red side, due to the fact most supports keeps dragon/bottom bush warded, causing your ganks to be that much harder. In mid lane you want to wait in one of the two outer bushes that surround the lane. When ganking top you want to do the same as bottom, go from tri bush because most the the time its warded on the river bush. Now being the jungler your job is to give an advantage to the lane, may it be a kill to the ad carry, killing the ad carry, pushing a tower ,burning summoner spells, whatever it may be, make your self a threat. You want to try and give your carry the kills,DISCLAIMER DO NOT LET KILLS GET AWAY IF THE AD/AP CARRY CANT KILL THEM only try and make it so they get the last hit so they get fed and making end game so much easier. After ganking the lanes racking up the kills and the gold its time you want to go back and buy your pretty Trinity Force. After trinity force its just about mid game and your starting to do more team fights this is where you change from ganker to sweeper/initiator. Now i build the massive magic resist because i like to get rid of the ad first so when the mages want to attack me i can take more pain then the average target. I Devastating Charge into the ad carry trying to isolate him from the rest of my team mates, also disorenting him (Physically not in the game) then i pop my Spirit of Dread i begin to spar with him keeping him from the rest of the team. You should kill him but if your on the brink of dying use your ultimate Onslaught of Shadows (try to aim the charge so it hits the team as well for the fear) and watch his hp vanish. at rank 2-3 your ult has a 90-70 sec cool down making it quite the spell to use. make sure to ultilize it in almost ever team fight. Also remeber you can charge through walls, use that to your advantage. Below is a map for reference begin to look at it and see the route of a jungler.

Ability Power Hecarim is a intresting card because only two abilities scales with ap, however its at a .8 scaling (80% of ability power)witch causes cataclysmic[/b] damage. You want to use your W when you can stay in range for the longest time as that does you entire damage. Lich Bane causes you do deal damage with your Q and other abilities making him not so useless. Lich bane is only reason that he is the slightest bit viable. save your ult for team fights because it can half an entire team in a second, not to mention your W on all nearby targets. You can almost heal to full within one W and your almost un-kill able. Make sure to time your auto attacks so that you can make the most out of Lich Bane. Other then that you can take quite the hits as a ap tank, you do the same thing as ap however you'll survive and kill more people.

Hecarim is a tough nut to crack, however it is very possible to counter him. His passive Warpath gives him AD based on his movement speed, however he losses these bonuses when he drops below his additional amount of movement. So slows counter his damage quite a lot. His jungle speeds are only possible by his Rampage And his Spirit of Dread After a while it causes him to go OOM rather fast. If you can counter his blue it slows down his speed dramatically. Make sure to watch your blue as well because he can take your jungle in no time. Also if you can move away from his Spirit of Dread and his Rampage his damage drops as well as causing him to become OOM. Good players will utilize the bonus Movement speed from his Devastating Charge ability, slowing him in the middle of that can greatly disorient the average player. If you flash after Devastating Charge You will be knocked back from your new location, so a well used flash can cause you to get even greater distance from Hecarim. His ult fears players AWAY from Hecarim if you run into him as his charging you can get feared away from him increasing the gap between you and him.

Thanks for reading! This is my first guide for a champion and i am open to suggestions and tips. I hope you learned a thing or two along the way and ready to take the fields of justice by storm. Remember to always ALWAYS ALWAYS get a blue ribbon for hecarim :P
Also Check out my Darius Build Here

Thanks for reading!

4/22/2012 update -Forgot to add the AP/ap tank guide as well, i will be updating as much as i can and when i get the chance to test things out.
4/27/2012 update- AP build/runes updated to better suit him, also solo top and new tank guide added. Also Countering section added