Karis was the King of the Gehena Pale, before it was destroyed and swallowed up by the forest. He was the father of Prince Menek and is unknown if he had any other children.
Though not much is known about his life or personality, in the story "The Legend Of Alcana", he became corrupted and obssessed with Fairy Cocoons and their silk, boiling the cocoons and the fairies they contained alive. This happened after his son, Menek brought home a gift from Alcana, whom Menek met when she was sat beside the Divine Tree, mourning for her mother. The gift itself was a fine silk cloth that Alcana wove herself and presumably, King Karis became obssessed with it's beauty and wanted more, whatever it took.
When Menek tried to show his father the error of his ways, he locked him away and was presumed dead by Alcana. Alcana throws herself into the marsh near the Divine Tree but comes across the Forest God Elrihm. Asking Alcana for a wish, she says that her love Menek was taken away from her because of the greed of the beasts of knowledge. Elrihm summons minions unto the forest which then swallow and destroy the Kingdom of Gehena Pale, presumably killing King Karis also.
This whole story is the premise of the game itself and the forest minions encountered in-game are the same minions that were spawned by Man's greed.
Though it is not explicitly mentioned in-game, Riketz may well be the reincarnation of King Karis, seeing as how Levant and Mahbu and reincarnations of Menek and Alcana, respectively.