Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Olaf is known for his ability to deal out physical damage quickly, his survivability, and in some cases his mobility. In this guide, I have built him to excel dramatically in all of these fields, making him an overwhelming force of destruction and desolation. I hope this guide serves to be helpful to anyone who may be interested in Building Olaf in such a way.
Greater Mark of Desolation - All of your damage is going to be physical, therefore, while increasing your attack damage is very important to achieve this, it is equally important to make sure you can get through your target's defense.
Greater Seal of Evasion - Dodge is actually pretty important to this build. Not only does it help with your survivability, but it helps with your mobility as well, because of the mastery. To illustrate, at times you may be chasing after an enemy champion. You run past their minions and continue your pursuit, meanwhile their minions are attacking you to the best of their ability. Odds are you will dodge at least one of their attacks, and this will cause your movement speed to increase. You should have no trouble catching that enemy champion, right?
Greater Glyph of Alacrity - Increased attack speed is also pretty helpful for for your damage output.
Greater Quintessence of Desolation - More armor penetration.
The masteries you can change to your liking. The only ones i really recommend getting are Nimbleness, Cripple, and Haste.
I think the items I selected are pretty solid, but feel free to experiment for yourself. I do recommend Stark's Fervor, as it is very helpful for this build. Frozen Mallet and Warmog's are also pretty nice to have here. But if you find yourself up against more mages, and you need magic resistance, then I would suggest trading the Ninja Tabi for Mercury's Treads, and either the Infinity Edge or the Phantom Dancer for a Banshee's Veil.
I chose to max out Reckless Swing first, because it is, in my opinion, his biggest source of damage. After that I recommend Vicious Strikes, to help you stay alive when Killing someone. I chose Undertow last, because it's a little underwhelming compared to his other skills. Obviously you should put points into Ragnarok whenever you get the chance.
I chose Exhaust and Ghost both to make sure you never lose someone when you are trying to kill them. you can obviously, also use ghost defensively to escape if you feel the need.
With this build you should be able to take on any enemy champion 1v1 without any real difficulties, and you should also be a huge asset to your team in team battles. In addition to that, you should have no trouble staying alive, and no one should ever be able to get away from you, nor should you have trouble getting away from anyone.
I apologize if this guide seems lacking in any way. It is my first guide, and i am definitely open for criticism. Thank you for reading, and good luck to all of you on the fields of justice!