File:Bloodmagesamwise.jpg

Summary
"Blood Mage" by Samwise Didier; Kael'thas in Manual of Monsters.

As Kael'thas Sunstrider
This blood mage art is named Kael'thas Sunstrider on the official website for World of Warcraft:
 * https://web.archive.org/web/20111028044936/http://us.battle.net/wow/en/media/artwork/warcraft3?view#/wc3-kaelthas-sunstrider
 * http://us.media.blizzard.com/wow/media/artwork/warcraft3/wc3-kaelthas-sunstrider-full.jpg

It's also named Kael'thas on Samwise Didier's deviantart page.

Source
The Burning Crusade Townhall: The Story So Far.... Source: https://web.archive.org/web/20071002114317/http://worldofwarcraft.com/burningcrusade/townhall/story.html