Hi, and welcome to My Olaf guide! I am going in depth with Olaf and how to jungle with him.
The thing that makes Olaf so strong in the jungle, is His axe! with the right runes and masteries, Olaf's axe can do massive damage both early game and late game.

Runes and Masteries are about Armor penetration, utility and sustain.
If you go 9/0/21 with olaf you get so much sustain in the jungle.
If you have Armor Penetration runes, you will deal tons of damage with your "undertow".
You may ask, "why do you go in the utility tree and not the Defence for keeping you alive in team fights or offence to clear jungle much faster", well i have the answer to that!
As i said earlier "Undertow" is your main damage output and the utility tree makes it much stronger, it gives more spell vamp, more cooldown reduction, even more experience, its also a great way to have smite up at all time.

The items on Olaf are very alternatives.
If the enemy team has alot of magic damage ofcourse you should go magic resist, but if they only are ad you should go armor. It depends really much on the enemy team.
The item build i have shown in the guide is for high AoE damage and magic damage.
And the second item build, is around hard AD damage or if the AD carry gets fed.

You have too max your Undertow, It is your main damage!
If you throw the Axe right in front off you with blue buff, it will have no cooldown at all.
That is so much damage lvl 9.

You have too go aggressive and snowball with this build, so You have too gank alot and make plays! (and if your olaf it should be pretty easy)
You have too get early kills, if You dont do that You have to farm alot too come back late game.
His ganks are very strong, if your lane intiates for you and you hit an axe, the target is sure to be dead!
The con about this is you have too pick up your axe all the time after you throw one, but if you are chaseing someone its pretty easy to pick it up.

Olaf farms so well with his Undertow, and with his Vicious Strikes he can keep himself up in the jungle, he never has too go back.
You have too make sure you have Vicous Strikes on when you use Undertow, it makes your undertow alot stronger and it gives alot more health.

Have fun playing Olaf, he is such a strong champion and he has alot of potential if you hit an axe, so make sure you hit those axe's when you play olaf!