Kael'thas Sunstrider, Lord of the Blood Elves
Powerful magic-wielding heroes of the blood elves.
A mystical hero, blood mages are adept at controlling magic and ranged assault. While they were still members of the Alliance, the blood elves began to turn to the darkest parts of magic, abandoning the water and frost spells of the Kirin Tor for the fire and heat of what some people fear to be demonic magic.Template:Cite
Many of the stoic high elves, reeling from the loss of their ancient homeland, Quel'Thalas, have given in to their hatred and despair and embraced the dark side of their magical natures. Calling themselves Blood Elves - these cold hearted refugees seek to expand their remaining magical powers at any cost - even if it means courting the infernal powers of the Burning Legion. Though still loyal to the Alliance, the Blood Elves' passions will lead them not only to the highest pinnacles of power, but to the darkest depths of madness.[1]
A blood mage in action
The most famous and the first of the Blood Mages was the Blood Elf hero Kael'thas. He commanded the Blood Elves in Warcraft III: The Frozen Throne's human campaign, leading them out of the Alliance and into Illidan's service.
Blood mages have many abilities among them are: 
[Banish], 
[Flamestrike], the use of Verdant Spheres and summon Phoenix.
See also: Warcraft III Units
Other Blood Mages
Eldin Sunstrider, Tanin Hawkwing, Lorn Bloodseeker, Aldos Firestar, Gilaras Drakeson, Hale Magefire, Kath'ranis Remar, Tyoril Sunchaser, Sylvos Windrunner, Tenris Mirkblood, Marakanis Starfury, Geldor Earthfire, Halendor Burnkin, Kelen the Destroyer, Bloodmage Lynnore, and Bloodmage Drazial