The stealthy rogue Kelen was well known for his ability to slip away from any pursuit and find his way out of even the most escape-proof traps. Only upon his death did the world learn that his secret was really in the glass-sheathed dagger he carried, Kelen's Dagger of Escape. The pommel appears to be fitted with an immense ruby, but this stone is also made of glass, a fact even a poorly trained merchant can recognize.
Other known Kelens are Kelen the Seeker (a random archmage) and Kelen the Destroyer (A random blood mage). Both are random generated heroes in Warcraft III: Reign of Chaos and Warcraft III: The Frozen Throne.
As Kelen the Seeker appeared as a (human) archmage and Kelen the Destroyer was a sin'dorei blood mage, it is unclear if these are all intended to be separate characters or the same character. It is possible that the archmage was a high elf who joined the sin'dorei movement, and even that this individual was also the renowned rogue. On the other hand, given the nature of archmagi, it seems unlikely that one would take time off from the arcane to become a famous thief. However, in the RPG multi-classing is quite common, and there are prestige classes that mix more than one class type. Ex. techno mage (tinkers and spellcasters). Kelen's Dagger of Escape could be found in Warcraft III during the bonus campaign, with a similar description. It should be noted that his dagger is enchanted with magical powers allowing escape.
Another Kelen the Seeker is to the side of Admiral Proudmoore at the invasion of Theramore by Thrall's forces, led by Rexxar. Nothing says it has some connection with Kelen found in Silvermoon City during the invasion of the Scourge.
The true nature of the character Kelen is that he was a Dungeons & Dragons character of one of the game developers, David Fried. He played the character in gaming sessions with other Blizzard members, and inserted the character's name into the two heroes and the artifact in the game.