We all have heard of him from Reav3 on the Yorick rework. Also he has a 
that has his name on it (possibly used by Kalista?) and Kalista is one of his top generals. But no one knows who he actually is. Is this a new champion confirmed?
The Ruined King was just a generic king who happened to be a powerful mage. Kalista was one of his generals, and Hecarim was the leader of a type of "special forces" known as the Iron Order. At one point, an assassin tried to do his job on the King, but ended up cutting the Queen with his poisoned blade. No one could cure Queen, so the King sent Kalista out to find a cure. Kalista eventually found a place called the Blessed Isles, a place that was hidden form normies, a place that had a secret password. The Master of the Isles saw the purity in Kalista's intent and gave her the password, telling her to bring Queen to the island, and then Master could heal her. By the time Kalista got back, Queen was already dead and King was going mad. Kalista had made a vow to not tell anyone about the Isles, but Hecarim (who was turning evil) convinced Kalista to tell King what she knew. So King and his fleet sailed to the Isles (with Queen's rotting corpse). King demanded that Master bring her back to life, but the guardians of the Isles told him that messing with resurrection is a "supremo bad idea to the max" - John Henry. King, who was completely crazy by now, became enraged and told Kalista to kill the guardians. Kalista refused, so Hecarim killed Kalista. Eventually, after killing a ton of people, King found the way to resurrect his wife. When he did however, she came back as a zombie who begged to be allowed to die. King then decided to commit suicide with his wife, casting a spell that would bind their souls together for eternity. The spell worked, but the Blessed Isles are a place of such concentrated magical energy that the spell gained incredible power, and kind of backfired, cursing the Isles into a place of undeath and pain. Hecarim was fused to his horse. Kalista was reborn as a spirit of vengeance. Some other guys turned into other things too.
Tl;dr - The Ruined King was a king who accidentally turned the Blessed Isles into the Shadow Isles. Now read the entire post.
http://2.bp.blogspot.com/-EqVmP4SzrAs/UI98sx_SL9I/AAAAAAAAJdE/BOOVpnFwrr0/s1600/alkty.png
-Edit: Downvoted without knowing: Its speculated, and almost confirmed, that the Male Altar is the Ruined King and her wife is the Female Altar... if you compare the quotes of them and the stories of the Shadow Isles, it makes perfect sense.
Read the Hecarim and Kalista lore. He was a king of a powerful nation before Demacia and Noxus was a thing (though likely during the time of Mordekaiser's reign of terror in Noxus domain), and his wife grew deathly ill. He called for help and Kalista went to find a cure but was too late. The queen was already dead and the king had gone insane. He forced her to bring him to the Blessed Isles despite Kalista being warned. They went there and the Blessed Isle refuses to return the queen from the dead. The king then commanded Kalista to kill the Blessed Isle men, but she did not. Hecarim and his men then stabbed through her and the king was brought to the secret to reverse death by Thresh, the maddened warden of the Blessed Isle's vault of forbidden objects. Almost as if it was all planned by Thresh, the king resurrected his wife and was repulse by what he had done to his wife, who begged for death once more. He then used a spell to reverse the reverse death, but the spell was enhanced hundreds upon hundreds of times over by the other objects within the vault and the spell instead killed and converted everyone on the Blessed Isle into undead abominations. Thus, the Shadow Isles were born all because of the Ruined King.
He was eggnivia Kappa
kalista's uncle
THE RUINED KING IS THE GUY THAT CREATED DYNAMIC QUEUE SEASON 6, AFTER THAT HE BECAME THE KING OF RUINING EVERYTHING. [slayer-jinx-wink]
The monk told tales of a time forgotten An ancient queen, now dead and mulch-rotten. Of her king brought low by sorrow and woe, Who came to this isle to bring back her life, But damned the world to endless strife, Spirits of death and carrion crow.
His magic unleashed a terrible scourge; Grim prelude to the Deathsinger’s dirge. Black mist rose up and doomed all to death. But spirits arose from every dead thing, Cursed to undeath by this grief-maddened king. He begged it all end with his very last breath.
A land once blessed, was ripped asunder, Split with lightning and beaten by thunder. Phantoms now mutter in graves enshrined. And banshees throng its haunted streets, Shrieking their woes of black defeats, A boundless curse upon all mankind.
-The Princes Lament http://na.leagueoflegends.com/en/featured/shadow-isles#/the-princelings-lament?_k=zquyoy
