Skeleton King

Ostarion the Skeleton King is a powerful melee strength hero, capable of taking plenty of damage before dying. His ultimate allows him to rise again, acting like an Aegis of the Immortal, making him especially difficult to kill. He also has a nuke that deals reliable damage and stun, and he is able to stay in his lane longer because of his passive lifesteal aura. He can become a hard carry in later stages of game depending on his farm.

Recommended items
Starting items:
 * Buying a Healing Salve or a Tango provides Ostarion with a decent amount of regeneration in the laning phase.
 * Buying a Clarity gives Ostarion more opportunities to set up kills early on with.
 * Starting with two Iron Branches give Skeleton King enough mana pool to cast two times at level 1.
 * A Quelling Blade is an excellent starting item for Ostarion as it allows him to get last hits easier. It also makes Mortal Strike hit harder against creeps and increases the effectiveness of Vampiric Aura when attacking creeps.

Early-game items:
 * A Magic Stick can sometimes be the difference between a death and a kill. Its active usually grants enough mana to sustain.
 * Boots of Speed provide an excellent boost of speed for any hero.
 * A Helm of Iron Will can be built into an Armlet of Mordiggian later on and gives extra survivability in the form of armor and health regeneration.

Core items:
 * Magic Wand provides the same kind of benefit as the Magic Stick does, but it also provides a small amount of attributes. It makes great use of the earlier bought branches, making room for new items.
 * Power Treads increases Ostarion's damage per second; attribute switching can also make his limited mana pool go much further if the treads are switched to intelligence.
 * Armlet of Mordiggian is Ostarion's main DPS item. It is also easy to negate the health drain with the help of.

Situational:
 * Desolator makes Ostarion's physical attacks to hit harder, especially against targets with already low armor. Vampiric Aura also benefits greatly from it, as it heals based on dealt damage after armor reduction.
 * Black King Bar negates Ostarion's main weakness: being chain-stunned and then burst down after . Furthermore, as long as he isn't disabled, he can keep hitting enemies, healing himself up with his aura.
 * Assault Cuirass increases Ostarion's damage output by increasing his attack speed and further reducing enemy armor. The aura from this item also increases his team's armor and attack speed. Since Skeleton King usually survives longer, the item's aura provides more impact.
 * Abyssal Blade not only gives Ostarion some health and a decent attack damage boost, it also gives his attacks a chance to bash and, on top of, another active stun which also pierces spell immunity, which is very handy as he is easy to run away from if his own stun is on cooldown.
 * Heart of Tarrasque gives Ostarion a great health, health regeneration and attack damage boost, making him even harder to kill and harder to ignore.
 * Heaven's Halberd gives Ostarion some evasion against enemies which rely on their physical attacks, and lets him cut off an enemy carry from their primary source of damage for a while.
 * Monkey King Bar increases Ostarion's attack damage, counters enemies with evasion abilities or items such as Butterfly or Heaven's Halberd, and provides him with a high chance to interrupt channeling spells when Hellfire Blast is not an option.
 * Divine Rapier is an excellent item for Ostarion to get due to it not dropping if activates upon death, thus making it less likely for him to lose it. When carrying the Aegis of the Immortal, Ostarion has to die 3 times to lose the Rapier. The great damage boost also increases his endurance by improving his lifesteal aura's returns.

Tips

 * Hellfire Blast is a very good nuke, allowing you to disable and slow at the same time. A perfect tool for ganks and team fights, it has a relatively low cooldown, so spam it if you have enough mana.
 * Learning Vampiric Aura during laning phase will shift the creeps equilibrium and you'll be forced to farm and fight under enemy tower. Good for pushing, but hurts your farm and puts you and your allies in disadvantageous position.
 * Always make sure to save some mana for Reincarnation, if you have less than 140 mana, you will not reincarnate. Soul Ring is handy for this purpose.
 * Hellfire Blast is usually maxed first and Reincarnation is taken as soon as possible. It's also recommended to take one or two levels of Stats on early levels to improve Skeleton King's mana pool and health, as both Mortal Strike and Vampiric Aura are not useful in lane (Due to the 6.79 patch Skeleton King has more base intelligence and has more mana to work with. This allows you to level up mortal strike earlier, increasing your dps for possible team fights).
 * Armlet of Mordiggian and Soul Ring are commonly built for Skeleton King because Vampiric Aura allows him to heal up quickly after taking damage from these items. With both items, at very low health, you can activate Armlet, then Soul Ring, then quickly deactivate and reactivate Armlet for what is essentially a free Soul Ring use.
 * Activating Phase Boots and Drum of Endurance at the same time will give you enough mobility to chase and kill.
 * Grabbing a Force Staff can help make up for Skeleton King's lack of mobility, and it allows him to jump closer to his targets to make up for the short range of Hellfire Blast.
 * Divine Rapier is a very strong item on Skeleton King, allowing him to take advantage of his great survivability (from Reincarnation and Vampiric Aura).
 * Refresher Orb is situational, as it allows you to potentially Reincarnate twice in a fight allowing you to be that much more useful in a team fight.
 * Although picking up the Aegis of the Immortal may seem redundant on Skeleton King, it is recommended if he is his team's main carry. This way, he has 3 lives to expend, and unlike Reincarnation, the Aegis doesn't require mana.
 * Try to initiate and tank as much damage as possible in team fights. If you are the last to die, nobody will be able to help you when you proc Reincarnation!
 * An alternate build known as wizard skeleton king is actually very viable. Due to the low cool down on Hellfire Blast, by choosing to forgo any points in critical strike for stats, as well as building arcane boots it is possible to have enough mana to constantly spam your stun. Moving from here directly to a dagon makes you a formidable ganker, and allows you to knock out targets in teamfights with less worry of dying compared to a typical nuker due to Reincarnation. Another benefit of this build is that it is very rare to not have enough mana for your ult.

Trivia

 * In DotA, Ostarion was known as King Leoric. Leoric was a recurring boss in the Diablo franchise, another game made by Blizzard. He is an iconic boss in Diablo; he reprises his role in Diablo III, through the alias "Skeleton King."