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, another nuke which temporarily drains the life of his opponents for himself, and is also 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.

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.
 * Mortal Strike's passive drastically increases Skeleton King's melee DPS. Synergizes well with Vampiric Aura, healing Skeleton King a big chunk of health every time he crits.
 * Mortal Strike's active effect also helps in making ganks faster by softening the opponent up, and can even be finished off with Hellfire Blast's DoT. Don't use it too early though, or the enemy might heal back right before dying!
 * Ideally, during late game, Mortal Strike's active should be saved for the last enemy in a team fight, because when it's on cooldown it will severely cut down Skeleton King's damage output.
 * 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 two levels of Stats on early levels to improve Skeleton King's mana pool and health. Alternatively take two levels of crit for slightly more dps early on, only do so if you really know what you're doing with Skeleton King though.
 * 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. It allows you to potentially Reincarnate twice in a fight allowing you to be that much more useful in a team fight as well as solving all of your mana issues.
 * 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.
 * It seems counter-intuitive, but you should try to initiate or try to soak all the damage; if you are the last to die, nobody will be able to help you when you proc Reincarnation!
 * Although some people think that Divine Rapier is risky even with Skeleton King, combining it with his passive critical and vampiric aura allows him to deal insane damage and heal insane amounts of HP, making it also an excellent item to improve his already enormous survivability.

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."