Olaf the berseker is really powerfull but mostly underestimated. And killing him while he is low on hp looks easy, can easily deceive and get you killed. This build will tell you mostly everything you need to know about olaf.

I go with armor penetration runes, critical damage runes and cooldown reduction runes. Olaf is purely ad so armor penetration runes are a obvious choice. Critical damage runes help a lot because you will be dealing lots of critical strikes. Flat cooldown reduction runes help a lot in the early game and makes your ulti a bit more viable for team fights. Ability cooldown reduction runes seem a bit strange i guess, but they work wonders in the early games, and that's when we ad carries must feed the most.

I mostly use 25/5 set up in the masteries, going full ad while taking some cd aswell. Some armor and magic ress arent a waste.

For item build, i start off with vamp scepter, even for laning. Seeing as Olaf attacks faster the lower on hp he gets, this will keep you healty and even if you are laning, get a few hits on mobs and get away healed. Next, i go for berseker greaver, then phantom dancer, then i finish emblem of valor, then blood thirster, then infinity for that nice crit damage and chance, then another blood thirster, and finnaly starks fervor. This will give you great life steal which will keep you laning well and really surprise your enemies while on low health with a burst of damage and not being able to die because of that life steal and attack speed. While on low hp, you as will get to about 2.3 attacks per second while offering great damage and critical chance. Notice the lack of hp items, you dont need them, because of your lifesteal, as long as you are hitting stuff, you cant die, and you will hit then hard because you cant be stopped because of your ulti. Enemies will look at you puzzled when you get an easy penta.

Take underthrow for the innitial slow and revealing area effect. It help avoiding ganks early. Next, take reckless *****slap and max it out as soon as possible because it is really powerfull in early game and you will be able to spam it because of your life steal. Vicious strikes is a great tool for killing. Max it out too when you can, but reckless swing is priority. Vicious strikes is really powerfull for staying alive in team fights and for junling too. If you are jungling, take it in level 1, but max reckless as prio because you will be ganking alot. Ulti ofcourse take in 6,11 and 18 level. Simple

I usually go with simple flash and ignite. Using flash can save your hide and let you catch up to your enemy and hit them with underthrow. Ignite is simple, gets you kills and lower the hp regen of your enemy( mainly help killing strong ls ad carries).

Jungling is simple, witht the attack speed and life steal, you will easily get both buffs on 3-4th level without using smite. You dont actually need those buffs, so leave them to some1 that need them more than you do, especcialy the blue buff. Kill the wulfs first, then go for the ghosts and finnaly the golems. They shouldn't make any problem for you. Always watch our for some good ganks and wreak havoc. Pay attention to your hp since you are jungling and you will be loosing a lot hp in the early game. Save enough for reckless swing to finish of your enemy if you decide you should try ganking.

Really simple. Open up the fight with underthrow and follow it up with vicious strikes. When u get close, *****slap your enemy with reckless swing and finish them off with auto attacks and further reckless swings. Ulti if needed. Dont be afraid to rush in 2v1 situations, or even worse, seeing as you have major life steal and being immune to disables, you will be very hard to kill while demolishing your foes. In team fight, target their mages first so that they couldn't dissable you after your ulti goes as dissables are the only things that can kill you, remember, hit to survive, the golden rule of this build. After you finish off their mages, take a pick, but mostly go for ad carries if they are dangerous, otherwise, help your team by attacking enemies that are most dangerous to them. Olaf has epic damage in the late game with this build. Wait until the fight starts, and then if it's off cd, flash in the middle of their team and immediately use your ulti and vicious strikes and simply squash them like the bugs they are. Remember, you are a viking, you are epic!

Olaf is really strong and he doesn't need much support and help from his team to be effective. WIth this lifesteal, you will be able to solo their tower by hitting their minions to heal a bit. Winning a game while your team if full of ******s and noobs is possible with olaf. As epic as he is, remember that you have low hp, despite your good life steal, be carefull that they dont burst you down.

Please do keep in mind that this is my first time building a guide so don't hate and flame if i messed something up please. And remember, im better at playing LOL than i am at building a guide. I win almost all of my games, and even if i dont, i always have good score with olaf, no matter how bad the game is, i always have more kills than deaths.