Well, HE is a nightelf soldier that fought during the War of the Ancients, until he was sucked into a portal that led to a demonic world, where he was captured and forced into slavery for about ten thousand years. After that, the demons took him to Draenor, where he was thrown in the orcish prisons. The orcs decided to make sport of him, so they had him fight in the arena, where he befriended an Eredar Paladin named Galathorn. The two of them escape when the orcs are ordered to march to the dark portal and fight off the humans coming through. They try to get through the portal and back to Azeroth, but that's when Ner'Zhul opens all of those other portals and tears the world apart.
Kelendras wakes up not too long afterwards, and has no clue what to do. So he wanders Draenor for a few years, and eventually finds Galathorn again. They both bump into the bloodelves on Draenor, at which point Kelendras meets Funestus, a bloodelf assassin who eventually becomes his arch enemy.
That's pretty much all i've got on his story so far. Kelen and Galathorn eventually get back to Azeroth during the WoW time period.
Below is a picture of Kelendras after he defeats a group of bloodelf rogues and takes their equipment.