Blood Elf Lieutenant

Blood Elf Lieutenants are blood elven units that are heavy melee. They appeared in the The Frozen Throne human campaign to aid Kael'thas Sunstrider. They made their appearance as units when being rescued by Kael'thas in the Dungeons of Dalaran.

Speculation
They may have been people like Thaladred the Darkener, Lord Sanguinar, Grand Astromancer Capernian or Master Engineer Telonicus.