Background story:

On an uncharted continent beyond Valoran's grasping clutches, the conqueror named Olaf was born to a long tradition of soldiers unlike most others. Berserkers, as they tout themselves, are warriors who channel fury deep from their cores, unleashing pure and savage wrath upon their enemies. This fearsome evolution is a product of their unforgiving home, Lokfar - a barren tundra where all creatures must vie bitterly for every resource. Olaf belonged to a seafaring clan known for ruthlessly pillaging any and all villages within reach of their dragon-crested longboats. The last time he saw his icy home, Olaf was embarking on an expedition to pioneer and plunder a distant land known only to legend. However, while underway, a terrible storm sprung up and Olaf and his crew were thrown to the mercy of a roiling and pitiless sea.

His ship destroyed, his crew nowhere to be found, Olaf miraculously washed up untold miles from ''friendly'' waters on the foreign shores of Valoran, south of Demacia. This unfamiliar place stunned and frightened the Berserker, for Lokfar is not privy to such potent magicians. Approaching them, Olaf hoped that they could use their mysterious powers to send him back to his people. A bargain was struck. Olaf would use his awesome prowess as a warrior to serve the unusual wars of Valoran in the League of Legends, and in exchange the sorcerers would find him a way to return. Despite his participation in the League, Olaf knows better than to trust the ''finger wagglers'' that run the Institute of War. He deliberately keeps details of his life and home from them. After all, with enough information, they would most certainly find the Lokfarians and dominate them as they have dominated all of Valoran, keeping both quietly -- and unwittingly -- in their thrall.

Beware the war cry of the Berserker. What surges toward you is unyielding, free from the shackles of reason.


So guys this is my first build so be good on me :))

Pros:
*Lot of health at the end of game so you can survive longer
*Very good damage
*Good health gain and regen
*He has good dance

Cons:
*easy to kill in early game or when he dont have lifesteal.
*Low armor and magic resist

Items:

Fist item is Faerie Charm, Rejuvenation Bead and 1 Health Potion,reason is simple you have mana and health regen and potion is always good.Why 2 tiamat?Because its great it gives you damage mana regeneration and health regeneration on begining so it will help you stay on your line to farm.Without farm you wont be good olaf because he need items to win and tiamat gives you splash atack,when you have 2 tiamats you will kill spawn creeps on 2 hits.Berserkes Greaves are good because of atack speed.You need health to survive as long as you can in fight and warmog is best option if you are good farmer.Atmas Impaler is good in combination with warmog and visious strikes you will gain lot of damage and good critical strike.Bloodthirster is good because of damage and lifesteal is you good farmed you should buy this its realy good on olaf. But if You arent so good farmed you can go starks fervor way its good for him too,this item gives you atack speed,lifesteal and hp regen whitch will help you in fights.

Skills:
First lvl is Undertow because its good to slow for first blood or if you escaping from first blood its usefull too.The i m going Vicious strikes and Reckless swing this skills is best on this hero to early game to do a lot of damage to enemy at 6,11 and 16 lvls take ulti because its wonderfull ultimate!You cannot be stuned,slowed,knocked to the air and a lot of **** like this!!!

Gameplay:

If you want to kill someone rush on him from bush throw Undertow when you will be close to him to kick his *** press "W" and "R" then do "E" to him ^^ use ghost and exhaust too it is good in combination with your ulti :)) For escape use your ulti + ghost if he still chasing you use exhaust on him or "Q" skill.
Try to farm as long as you can,better untill you have warmog or untill lvl 14-15.

Comment please,i will update this guide.And sry for bad enghlish i m not native speaker.

Skills:
Undertow - Olaf throws an axe into the ground at a target location, dealing damage to units it passes through and slowing their movement speed. If Olaf picks up the axe, the ability's cooldown is reduced by 6 seconds.
Olaf throws an axe to a target location, dealing 65/110/155/200/245 (+) physical damage to units it passes through and slowing them by 24/28/32/36/40% for 2.5 seconds.

If Olaf picks up the axe, the ability's cooldown is reduced by 6 seconds.
Cost
55/60/65/70/75 Mana
Range
1000
Vicious Strikes - Olaf's attack damage is increased, based on his health, and he gains massive lifesteal and spell vamp.
For 6 seconds, Olaf's attack damage is increased by 10/17/24/31/38 (+ [0.5% of maximum Health]) and he gains 9/12/15/18/21% lifesteal and spell vamp.
Cost
40/45/50/55/60 Mana
Range
700
Reckless Swing - Olaf attacks with such force that it deals true damage to his target and himself.
Olaf deals 100/160/220/280/340 true damage to his target and inflicts 40/64/88/112/136 true damage to himself.
Cost
50/50/50/50/50 Mana
Range
325
Ragnarok - Olaf is immune to disables, has increased armor penetration and reduces incoming damage.
Active: For 5/6.5/8 seconds, Olaf is immune to disables and reduces incoming damage by 20/30/40.

Passive: Olaf has 10/20/30 increased armor penetration.
Cost
100/75/50 Mana
Range
400
Berserker Rage - For each 1% of health missing, Olaf's attack speed is increased by 1%.[/color]

Good luck and have fun guys!!!