Garen is easily one of the most satisfying characters to play in League due to his Ult, and the power spike it gives him at Lvl 6 is enough to warrant a "Surprise Muthaf**ka" sound effect if you do upload gameplay to youtube.

Since he is available from the Tutorial, Garen is a figure akin to Street Fighter's Ryu. He teaches you the basics, and you can either choose to move on, or to improve on him. This also leads him to a shared problem: everyone knows how to counter him.

Now before you immediately exit this guide saying "Not even the guy who plays him has any faith in him, so why should I?", I'll tell you this. Garen can be countered, but countering him takes away someone from the enemy team who could counter your ADC or APC.

Besides, his Ult can hit harder than a Falcon Punch (when used properly), and who doesn't like that good guy feeling you get for playing the hero?

-VERY Tanky lategame: Almost impossible to kill without a large amount of stuns/snares. As soon as he puts some distance between himself and that fight, he's gonna be right back to full health soon enough.
-Unlike most Tanks, Garen has a good early lane bully game.
-Garen counters Riven. Enough said.
-Garen trades favorably with almost everyone in the game.
-His CC:Silence can stop ability reliant enemies dead in their tracks.
-Garen's ability to break slows gives him the element of surprise.
-Courage and Demacian Justice (when combined with the sudden surprise of Flash) give Garen an insanely good Tower Dive game. Low health enemies are especially vulnerable.
-Judgement can dish out high amounts of damage to multiple enemies at once. Very useful when on a team with trapping abilities such as Thresh, Veigar, or Jarvan IV.
-Courage allows you to tank enemy abilities for your team without sustaining too much damage.
-Demacian Justice kills low health runners with ease.
-Garen has good map mobility with high CDR.
-Garen can run through enemy lines to kill carries quickly.
-Garen makes good use of bushes.
-If one or more enemies counter you, that's fewer people left to counter your Carries.
-Makes quick work of towers late game. Courage also allows him to stay a little longer, even when there are enemy champs nearby or the tower is targeting you.

-Low lategame damage makes you reliant on your team for most engagements.
-Almost entirely ability reliant: AA is only useful against people who are actually fighting you and not running. If Courage is stopped before activation then Garen can still be killed somewhat quickly by a 5 man team.
-Demacian Justice can be stopped if the enemy breaks line of sight before your sword hits the ground.
-Using Decisive Strike at the wrong time can be fatal against teams with slows.
-Garen isn't the tankiest guy on earth: He can't survive meat grinds alone, so be sure to have your team behind you.
-No good escape abilities: practically forces you to take Flash with you.
-Doesn't fare too well against other Tanks...
-Everybody has their counters... (Looking at you, Satan.)
-Because Garen's been around for five years, and that everyone has generally played him at some point, everyone will know how to counter him. The question is if they'll focus on you.

Against most champions in the game (especially among those who are found often up top), Garen can harass effectively at lvl 2 and start killing around lvl 4. Decisive Strike at lvl 1 deals out a good amount of damage without having to commit too much. At lvl 2, Judgement puts out a decent amount of damage against people who aren't really tanky. At lvl 4, you should have 2 and 2 in DS and Judgement. This can lead to some early kills. It's around there that you'll take your first back.

It's around here that the build begins to reach it's highest point in AD. You'll be leaving some bruises on your opponents, and someone moving a bit too close to your minion wave is in for a world of hurt. If you've destroyed the enemy's outer turret, then it's OK to Flash and Ignite for a kill, given that the enemy champ is around the middle of the lane.

Garen's damage falls off around here, so that's why you make the transition from fighter to tank. Charge through the enemy line to distract them and cause havoc (as well as kill the enemy carry). You always want to have your buddies to back you up. Charging in alone is a really pathetic way to die...

IF you're going to push lane, AND there's no one around (they must be accounted for by your teammates, though you can probably handle a non-fed champ), a good strategy is to use Decisive Strike on the Siege Minion and then use Judgement to finish off the group. This generally rewards you with several last hits, and if you build CDR, then you won't have to worry about your cool downs too much. Aside from that, just do the usual Stand-behind-your-minions-and-autoattack-for-lasthits kinda thing.

Garen is a dynamic character who transitions between two roles during a match. He can deal with enemy assassins very well and can immediately make quick work of an enemy carry. His early game is amazing for a Tank and he can shut lane opponents down (except Satan himself, who can't be shut down at all simply because he is Satan). You will be very reliant on abilities for damage (especially his E), and even some of your tankiness, so maxing your CDR is very important.

-1.0.0: Released
-1.1.0: Updated for Black Cleaver Buff (5/3/15)
-1.1.1: Updated Matchups to attune for Cleaver Buff and Spellcheck trolls.